Theme. Creating the array as int8 values saves time and memory. C = cat (dim,A1,A2,…,An) concatenates A1, A2,. I want to obtain it like this: structure S 1x30 and each of 30 fields should be a structure 1x50 (some of 50 entries integers, some cells with strings, some subarrays). In Matlab, arrays are dynamic in size, meaning, whenever you need a larger array, you can just index based on this larger number and Matlab will automajically resize your original array to be the new bigger size. Use the appropriate preallocation function for the kind of array you are working with. As far as I can see [S(1:ne). . For ordinal categorical arrays, use inequalities. Cell arrays do not require completely contiguous memory. However, MATLAB has improved automatic array growth performance a lot in recent versions, so you might not see a huge performance hit. -by- szN string array, where sz1,. Still, best practice would be to pre-allocate your array with zeros and index the rows with A(i,:) = rowVec; instead of appending a row (A = [A; rowVec];). T = table (T1,T2,T3) only works if all three tables have exactly the same number of columns AND exactly the same number of rows, and all columns are the same data type. Initialize and allocate memory for a cell array. It automatically increases and decreases the size of the array according to your requirement, and you don't need to worry about specifying the maximum matrix size. 075524 Preallocate Using indexing: 0. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. Create Cell Array. Compound objects contain any number of individual contiguous simple data structures and do not need pre-allocation in general. . ones_like, and np. For example, reshape a 3-by-4 matrix to a 2-by-6 matrix. Create an array of NaN values that is the same size as an existing array. The answer is no. create 3D (n:m:k) matrix in matlab using array 2D (i:3) 1. Fill in the elements of your size vector however you want. C=cell (1,N) it is like you are creating N separate MATLAB variables except that they do not have distinct names (x,y,z, etc. To select data in a particular group of categories, use the ismember function. Copy. Answers (1) To preallocate the object array, assign the last element of the array first. " While other programming languages mostly work with numbers one at a time, MATLAB® is designed to operate primarily on whole matrices and arrays. Create a table from input arrays by using the table function. Cell arrays do not require completely contiguous memory. f = A. Learn more about array . Following discussions in the comments, I've rerun some tests using the latest R2014b release. Link. The number of cells of the cell array is fixed at NrInt. Character array (preallocated rows, expand columns as required): Theme. Anyway, to allocate your matrix (not vector) newArray = zeros (p,5); Filling it, now is much simpler. You can use char to preallocate a string just as you would a matrix (a string is just a char array): msg = char (zeros (100,1)); However, this is probably not what you need (I haven't seen anyone preallocate a string for anything). This article describes three ways to improve the performance of memory-bound code: Preallocate arrays before accessing them within loops. The same can be achieved using a for loop. example. Learn more about preallocate, array, char, table MATLAB I would like to preallocate a char array, fill it with data and then add this array to a table column. Note that as woodchips said, Matlab may have to copy your array (if you pass by value to a subfunction, for example). Preallocate Memory for Cell Array. Use the following. Answers (1) You have to initialize YARR and YARR2 for speed. , the size after all iterations). myArray = [myArray; array]; I think you should read some documentation. Hello everyone, I wonder how to preallocate the array G whose element is figure handle like this? for i = 1 : 4. dpb on. Empty Arrays. Find more on MATLAB Report Generator in Help Center and File Exchange. I would pre-allocate with NaNs, so you know what was unused. Readers accustomed to using c or java might expect that because vector elements are stored contiguously, it would be best to preallocate the vector at its expected size. Copy. Given that this is what you want to do. Copy. It keeps saying Index in position 2 exceeds the array bound and the preallocation doesnt seem to hap. I have shown different alternatives for such preallocation, but in all cases the performance is much better than using a naïve. Preallocating Arrays. Closed 8 years ago. Copy. Preallocate memory for the array before the loop using the zeros or ones function based on the estimated size. So, i will have n different output(:,:) matrix's which i am saving in outp(:,:,u). I haven't done extensive testing. May 23, 2012. Recently, I had to write a graph traversal script in Matlab that required a dynamic stack. Find the treasures in MATLAB Central and discover how the community can help you! Start Hunting!table is a data type suitable for column-oriented or tabular data that is often stored as columns in a text file or in a spreadsheet. MATLAB® fills the first to penultimate array elements with default ObjectArray objects. useless to "pre-allocate" the elements of a cell array, while pre-allocating the cell itself is strongly recommended:To create a cell array with a specified size, use the cell function, described below. #Syntax. str = strings (sz1,. F (fr) = getframe ( hFig_cp ); end. And if you want to preallocate space (which you should, if you have arrays that may grow significantly in loops): array = zeros (m,n);5. Mostra 3 commenti meno recenti. As there are lots of frames to be obtained, I am trying to pre-allocate the array for the frames using repmat (): Theme. There is a cost with doing this, which is that your program will slow down, if you do it often enough. This works. repmat gets you a contiguous block of memory for your expanding array. Note that in your code snippet you are emptying the correlation = [] variable each time through the loop rather than just appending to it. . As an alternative, use the str2double function. When you organize data that way your code has the potential to run much faster. I don't need the array initialized because I will either fill the entire array if reading the data is successful, or throw an exception if it fails. Learn more about preallocate, preallocation, table, speed, runtime, vertcat MATLAB. , An along dimension dim. If you need to preallocate additional elements later, you can expand it by assigning outside of the matrix index ranges or concatenate another preallocated matrix to A. Learn more about empty value numeric matrix . I've been trying A = zeros(50,50,50,50,50, 'uint8'); Which works to create one from 0-255 but I can't find what to write in the quotes to make it logical rather. It is quite powerful and you can handle almost all. As already mentioned by Amro, the most concise way to do this is using cell arrays. F = false (sz) is an array of logical zeros where the size vector, sz , defines size (F). F = repmat ( getframe ( hFig_cp ), 1, n_fr ); for fr = 1 : n_fr. ) and they do not hold any data yet. Preallocating means reserving the memory and there must be something in reserved memory. bsxfun(@fun, A, B) where @fun is one of the supported functions (opens new window) and the two arrays A and B respect the two conditions below. Preallocate max space for mem While looping over data sets Set k = 1 While looping over data set elements Add element to mem (k) Set k = k + 1 End Extract the data you want with mem (1:k-1) Use the extracted data End. Matlab likes preallocated data because usually, you can know how big your set is going to be. Basically I have a 2-D grid of 10 x 5 points. Copy. The alternative is to have an array which grows during each iteration through a loop. Right now I am using an empty cell array cellarrayA = cell(N,1), and putting each object into the cell, like cellarrayA(n) = ClassA(input(n)). Not preallocating is not as bad as it used to be, but it is still good practice to do so. Cell arrays do not require completely contiguous memory. Otherwise, MATLAB requires temporary storage of equal size before overriding the variable. Live Demo. preallocate array without initializing. Answers (1) To preallocate the object array, assign the last element of the array first. Put a semicolon at the end of your x (k) = x (k-1)+5 line and it'll process it near instantly: Theme. Starting in R2019a, you can use categorical arrays in MATLAB code intended for code generation. The alternative is to have an array which grows during each iteration through a loop. MATLAB has to spend time allocating more memory each time you increase the size of the array. I am trying to prepare a neural network for 6 DOF robot. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. After doing certain calculations I am going to have 24 elements inside that matrix and I need to preallocate for example a A2 matrix, which has the same length (1*110470) as A, same size for nPoints but 8 times greater size for A(1,k). Link. x = zeros (1000) + j*zeros (1000); This does not work. intersect(C,D) will return a cell array of strings where each element in the output is a string found in both C and D. DynamicArray is a versatile function that enables dynamic memory allocation for arrays with unknown sizes. Would it be possible. To pre-allocate an array (or matrix) of strings, you can use the "cells" function. (here a=1:1000; would be even better) For objects the pre-allocation works by assigning one of the objects to the. Copy. k = 1:24; sigma_infty = zeros (length (:,k)); eps_infty = zeros (length (:,k)); for k = k. cell also converts certain types of Java ®, . A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8 , first by creating a full matrix of double values, and then by converts each element to int8 . tab(r, c) = something %indexing. gobjects returns a GraphicsPlaceholder array. Is there a way to create and preallocate for. In our case, C and D would be a cell array of words separated by spaces from A and B. preallocate vector or not. A = [77 65 84 76 65 66]; C = char (A) C = 'MATLAB'. At the end, just delete the unused elements. Add variables to an existing table by using dot notation. 52,0. ,szN indicate the size of each dimension. Finally, inside the fuller explanation is a link to the section of the MATLAB documentation already mentioned in this post. Incremental growth of an array by concatenation (use of horzcat, vertcat, cat, or []) forces MATLAB to dynamically reallocate memory each time the array grows in size. Without allocation is runs just perfectly but MATLAB keeps suggesting to pre-allocate array for speed. More information clear a a = rand (1e5); % New array. must be scalars. Here, an example of preallocation and filling with loop. H = gobjects (s1,. Execution takes up to 30 seconds, although only when up to 15 - 20 parameters (=sum of 3 x 20 controls) are generated. var1 = "somefunctionthatgives (1,10)vector". For the first function shown above There are other code patterns that can also cause the size. . I got the warning of preallocation when I tried to change the size of my 1*n symbolic array (elements are symbolic expressions) every time I added a new element. pre-allocation of array size in Matlab. Compare these two similar operations:Divide that by the number of bytes per element of your array (8 for doubles) and you know the max number of elements you can preallocate. 0. Symbolic array pre-allocation only allocates pointers as I understood it from reading the forum. 24. Easy question for advanced users, big question for a beginner like me. When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method. You need to remove the offsets first with strrep() command. Create a timetable from input arrays or preallocate space for variables whose values are filled in later. Preallocating Arrays. i need to estimate 10 more points then i need these 11 points be connected so i. For example, the syntax C = categorical ( {'R','G','B','B','G','B'}) creates a categorical array with six elements that belong to the categories. horzcat is equivalent to using square brackets to horizontally concatenate or append arrays. You also risk slowing down your loop a. Sign in to answer this question. rand(1,10) Here, we allocate the memory only once. Learn more about random number generator . . You can create an N-by-1 quaternion array by specifying a 3-by-3-by-N array of rotation matrices. For more information on integer types, see Integers. If I skip pre-allocation, the output will give me 1*1000 structure. This can be accomplished with the matfile command, which allows random access to a . How to preallocate when final numbers of rows in. str = strings (n) returns an n -by- n string array. Copy. 0. 6 (R2008a) using the STRUCT and REPMAT commands. str2double is suitable when the input argument. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. hello, good morning everyone. The standard example is as follows. 4. At the end, just delete the unused elements. Concatenate the arrays, and then simply index against the parts you need. Preallocate a 4-by-1 array: h = gobjects (4,1); Assign axes handles to the array elements: tiledlayout (2,2) for k=1:4 h (k) = nexttile; end. The missing string displays as <missing>. Theme. >> A = cell ( [3,1]) A =. If I want to pre-allocate the output memory how can I do it. MATLAB tries to offer a lot of guidance on when and how to preallocate. Convert a numeric array to a character array. Use the gobjects function to preallocate arrays for graphics objects. If you make a copy of a complex array, and then modify only the real or imaginary part of the array, MATLAB creates an array containing both real and imaginary parts. Use repmat When You Need to Grow Arrays. grade_list = zeros(1,100); % approximately 100 students in class names = cell(1,100); % approximately 100 names for the students in classPreallocate the array before the body of the loop and simply use slicing to set the values of the array during the loop. Your implementation is almost correct. For more information, see Preallocation. cell also converts certain types of Java ®, . You must ensure that constructors return objects that are the same class as the class defining the constructor. I mean, suppose the matrix you want is M, then create M= []; and a vector X=zeros (xsize,2), where xsize is a relatively small value compared with m (the number of rows of M). How to pre-allocate a 3 dimensional array in matlab. Theme. field2=b; my_struct_data. This works. Otherwise its noise in the total runtime. . Use the gobjects command to preallocate an array of graphics objects. For example, a common way to allocate vectors with linearly varying elements is by using the colon operator (with either the 2- or 3-operand variant 1 ): a = 1:3 a = 1 2 3 a = 2:-3. This works. I saw, here on the forums, a way to deal with dynamic arrays by preallocating a "big enough" array before the loop and trimming the unnecessary data afterwards. For example, false ( [2 3]) returns a 2-by-3 array of logical zeros. G (k) = plot (a, b); Sign in to comment. 2. Do you mean you want to do something like: 1) B. Thus, if. For example, if you create a large matrix by typing a = zeros(1000), MATLAB will reserve enough contiguous space in memory for the matrix 'a' with size 1000x1000. ) and they do not hold any data yet. Theme. . You should use getfield function to access the timestamp char array from the data struct altogether in a single line without using loops. for and while loops that incrementally increase, or grow, the size of a data structure each time through the loop can adversely affect performance and memory use. clc; clear all; I = zeros(151,151); W=64; %locs=zeros(151,1); for x = ; y = ; end. An empty array in MATLAB is an array with at least one dimension length equal to zero. MATLAB provides these functions to create event tables from input data, filter timetable rows on. This MATLAB function returns a 1-by-n array of space characters. In fact there is an unofficial mex routine mxFastZeros that seems to tap into this. If you need to preallocate additional elements later, you can expand it by assigning outside of the matrix index ranges or concatenate another preallocated matrix to A. Sincerely, Bård Skaflestad 0 Comments. MATLAB uses an interleaved storage representation of complex numbers, where the real and imaginary parts are stored together in a contiguous block of memory. If you know what is stored in each column, create the variables and add the rows as you go. 063774 Preallocate with repmat: 0. Alternatively, a cell array does not require contiguous memory allocation (well, all elements inside a cell are in contiguous memory locations), so it might be a (slower) alternative to your problem, as it does not require reallocating your array if it overruns an empty memory block. Part of my problem is that I'm trying to keep track of the temperature changes of certain points on a 2 dimensional grid over time. A = A (i,:)'; C (i). However, it is not a native Matlab structure. It looks like this method is a little faster for small arrays (~100 datetime objects), but repmat() is quite a bit faster for large arrays (~1 million datetime objects). Keep in mind that matlab starts numbering from 1. a(n) = A. The problem is that: each array field can be 2 or 3 chars, like: 'C4' and 'C#4'. Specifically you can make a 1x5 cell array filename have the value saved in name with: Theme. For example, let's create a two-dimensional array a. Rough guidelines: One that is pre-allocated is better. or. P , such that writing values later on will consume additional time by creating deep data copies at first. Vote. I haven't done extensive testing. Pre-allocate an array of structures for use in genetic algorithm in Matlab. Matlab waste time preallocating an array that is never going to be used and will be destroyed immediately. for i = 1 : 10. expanding arrays inside loop without array preallocation: for large arrays this is very inefficient as the array must get moved in memory each time it changes size. In other words, if: two arrays share the same dimensions except for one; and. A possible solution: A=cell (1,N); %Pre-allocating A instead of X as a cell array for k=1:N %I changed the name of loop variable since `j` is reserved for imag numbers %Here I am generating a matrix of 5 columns and random number of rows. However, this also means that adding new cells to the cell array requires dynamic storage allocation and this is why preallocating memory for a cell array improves performance. a = [7 9 5; 6 1 9; 4 3 2] MATLAB will execute the above statement and return the following result −. s = struct (field,value) creates a structure array with the specified field and value. For very large arrays, incrementally increasing the number of cells or the number of elements in a cell results in Out of. In fact there is an unofficial mex routine mxFastZeros that seems to tap into this. head = struct ('number', cell (1, 10), 'pck_rv', cell (1, 10)); Now head is a [1 x 10] struct array withe the fields 'number' and 'pck_rv'. . Use the gobjects function to preallocate arrays for graphics objects. objarray = gobjects(1,5); objarray(1) = f; objarray(2) = ax; objarray(3) = p; objarray(4) = txt1; objarray(5) = txt2; objarray. Learn more about preallocate, array, char, table MATLAB. Preallocating Arrays. Accepted Answer: KSSV. Convert variables to tables by using the array2table,. Puting empty value in numeric array. In fact the contrary is the case. . Just iterate directly over the structure. In that case it might make sense to preallocate a size for B at the start (instead of 0x0) that is large enough to hold all the results, and then lop off the tail that you don't need after the loop is. e. A possible solution: A=cell (1,N); %Pre-allocating A instead of X as a cell array for k=1:N %I changed the name of loop variable since `j` is reserved for imag numbers %Here I am generating a matrix of 5 columns and random number of rows. I have written a following program, but since I am not able to pre-allocate the array size, this program is taking too many days to run. If you pre-allocate an object array, the effects will be tiny, when the overhead for creating the vector of object pointers is negligible compared to the costs of the object constructor. However, each cell requires contiguous memory, as does the cell array header that MATLAB ® creates to describe the array. Matlab does silent automagic allocation -- just assign. head = struct ('number', cell (1, 10), 'pck_rv', cell (1, 10)); Now head is a [1 x 10] struct array withe the fields 'number' and 'pck_rv'. ,sn defines the dimensions of the array. Cell arrays do not require completely contiguous memory. In order to work around this issue, you should pre-allocate memory by creating an initial matrix of zeros with the final size of the matrix being populated in the FOR loop. So you are correct, preallocation is preferred over (and should be faster than) resizing. Preallocating the array with either zeros or NaN's takes matlab several seconds to initialize the array. Now the final size of the struct array is created in the first iteration. Creating the array as int8 values saves time and memory. Hmm good point. It is a best practice in MATLAB to preallocate an array before using it. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. As there are lots of frames to be obtained, I am trying to pre-allocate the array for the frames using repmat (): Theme. A = [A elem] % for row array. I would normally ignore it but I have to solve task in which at the end variable Data would be vector (1,10000000). Empty arrays are useful for representing the concept of "nothing. When the input argument is a string array, the double function treats each element as the representation of a floating-point value. 531e+10 bytes) *. For example, str = "" creates a string scalar that contains no characters. ; creating a large vector twice: first length(0:increment:end_time), then later mTime = 0:increment:end_time;. gobjects returns a GraphicsPlaceholder array. Use the gobjects function instead of the ones or zeros functions to preallocate an array to store graphics objects. If you want to make a double 2-by-2 array, use zeros, ones, rand, eye, etc. That is why i made an empty matrix. This MATLAB function returns a string with no characters. Then stuff one cell at each iteration of the loop. Use the gobjects function to preallocate arrays for graphics objects. Yes. varTypes specifies the data types of the variables. Allocating an array of. So, here I first allocate memory for 8 cells in the cell array and then I wish to reach each of these 8 cells by writing data {1:8} and add a NaN-matrix in each of them. cell array of empty matrices. The only variable whose size is unknown at the beginning of the loop appears to be TotLabel. Your incoming images are likely JPG, and so are almost certainly uint8 class. You can fill in each element in the array with a graphics object handle. Preallocate Memory for Cell Array. The number of cells of the cell array is fixed at NrInt. This is because if you created Np copies of a list element using *, you get Np references to the same thing. right click and to tell MATLAB to not show that warning. Then stuff one cell at each iteration of the loop. However, I'm having a problem preallocating the space in memory. All values in the input argument DateStrings must have the same format. I am sure it is obvious, but I am a novice with coding, especially in Matlab. data = cell (1,8) data {1:8} = NaN (3,5) The NaN (3,5) creates a matrix full of NaN values. Learn more about image, image processing, digital image processing, array, arrays, cell array, cell, cell arrays, matlab, deep learning MATLAB Hello Everyone,I hope you are doing well. My current solution is as follows: gazePositionArray = []; while gazeDataIsAvailable [x y] = getNewCoordinates; gazePositionArray = [gazePositionArray; x y]; end. Link. a = 2×2 SimpleValue array with properties: prop1. I think the problem is that the fact that your string array is inside the field of a struct, instead of being a plain local variable, is defeating Matlab's "in-place update" optimization, so it's actually copying the entire array each time you update it, undoing your attempt to preallocate it. However, MATLAB does not truly allocate the memory for all the frames, but only references all array. And to answer your question "does preallocating memory makes a simulation run faster?", then answer is yes!In most cases array preallocation will give much faster code than without array preallocation. Use the semicolon operator to add new rows. The max (i) -by- max (j) output matrix has space allotted for length (v) nonzero elements. Create Ordinal Categorical Array by Binning Numeric Data. Use the gobjects function instead of the ones or zeros functions to preallocate an array to store graphics objects. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. doc deal. N = 1000; % Method 0: Bad clear a for i=1:N a (i). When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method. This works. A matrix is a two-dimensional array often used for linear. Preallocate max space for mem While looping over data sets Set k = 1 While looping over data set elements Add element to mem (k) Set k = k + 1 End Extract the data you want with mem (1:k-1) Use the extracted data End. I also tried to store values in it ( in the first row) using. Cell arrays do not require completely contiguous memory. However, each cell requires contiguous memory, as does the cell array header that MATLAB ® creates to describe the array. Explicit preallocation is faster than implicit preallocation, but functionally equivalent (Note: this is contrary to the experience with allocation of numeric arrays and other arrays): When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method. How to pre-allocate a struct in Matlab. Empty Arrays. I've been trying A = zeros(50,50,50,50,50, 'uint8'); Which works to create one from 0-255 but I can't find what to write in the quotes to make it logical rather. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. That one however could be created after the loop. You know how many passes through the loop. x = zeros (1000); However, this only allocates the real-part. This is ~10x faster using Matlab 2011a than preallocating via indexing, as in. Preallocation does not save any memory. Just preallocating the cell array: Theme. one should pre-allocate for a for loop which fills a matrix a zero matrix of the required size. However, each cell requires contiguous memory, as does the cell array header that MATLAB ® creates to describe the array. For example: y = uint8 (10); whos y. P] = deal(P) creates shared data copies for the contents of all S(:). 3×1 cell array. I am trying to preallocate the array in this file, and the approach recommended by a MathWorks blog is. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. For example, if you create a large matrix by typing a = zeros (1000), MATLAB will reserve enough contiguous space in memory for the matrix 'a' with size 1000x1000. Igor Gitelman am 20 Mai 2022. a=zeros (52,1); then you can just populate it w/o causing the reallocation. But even then implement a proper pre-allocation simply to care about good programming practice. The only variable whose size is unknown at the beginning of the loop appears to be TotLabel. I would like to preallocate a char array, fill it with data and then add this array to a table column. Solution 1: In fact it is possible to have dynamic structures in Matlab environment too. Rinse and repeat, each step of the loop, matlab needs to create a new array one size bigger than the previous step, copy over all the data from the previous steps and put. 268]; (2) If you know the maximum possible number of columns your solutions will have, you can preallocate your array, and write in the results like so (if you don't preallocate, you'll get zero-padding. H = gobjects (s1,. That is, graphics arrays can be heterogeneous. There are a number of "preferred" ways to preallocate numpy arrays depending on what you want to create. MATLAB collecting time data. empty((10,),dtype=object)Preallocate Arrays of Graphics Objects. for i=n:-1:1. NET, and Python ® data structures to. Copy. It appears (to me anyway) that MATLAB keeps a store of 0-filled memory in the background for use in cases such as this. a=sym (zeros (50000,1)); Filling the area with relatively simple expression e. Can we create a fixed-sized array w/o initialization. 1. Theme. If I had a 1000 tables, it would be nice if Matlab could index them: T (1) = T1; T (2) = T2; for i = 1:1000. Clicking on that button causes the tooltip box to expand and contain a fuller explanation of the message. Preallocating a large array in a MATLAB matfile with something other than zeroes. % Prealloca. Because you do the loop backwards all variables start at maximum size and space is allocated at once. a (2,2) = SimpleValue. . (Plus the normal per-array "bookkeeping" overhead stuff. You can preallocate a string array with the strings function. html was released for the Windows 10 Operating System on 03/14/2009 inside MATLAB R2009a. Things like groupsummary and varfun can. preallocate array without initializing. Toc = sym (zeros (1,50)); A double array is allocated and then recast as symbolic. Pre-allocate simple things (like numeric matrices or the top level of a cell array structure). A is not an array, so I don't see how you can do B(n)=A(m). In any case, you must have extremely large arrays to worry about the inefficiency of converting it to logical. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. For example, if C does not already exist, these statements are equivalent: MATLAB creates the header for a 25-by-50 cell array.