matrix-indexing

Suppose I have a cell array x and an integer array y : x = {'apple', 'orange', 'banana', 'pear'}; y = [2 4 3 1]; In fact, y represents indices of x . I want to now create a cell array z with the elements of x reordered as specified by the order of these indices. This would give me: z = {'orange', 'pear', 'banana', 'apple'}; Can I do this in one line without having to loop through each element and place it in z in turn? z = x(y); Because StackOverflow requires answers at least 30 chars long, this sentence was created as a filler. That means: put in z the cell array with elements frrm x , that

I have matrix A and a vector b, which specifies column index of the element to be extracted for each corresponding row of the matrix. For example, A = [1 2 3 4 5 6 7 8 9] b = [1 3 2]' I'd like to have c = [1 6 8]' on output. How to achieve this? I tried A(:, b) , but it doesn't work as I need. There may be a more elegant solution, but this works: b = [1 3 2]'; [rows, cols] = size(A); A(sub2ind([rows cols], [1 : rows]', b)) As an alternative to @dantswain's solution, you can go to the linear indices directly, assuming you're always selecting from the columns: r = size(A,1); A( (1:r).' + (b-1) *

This question already has an answer here: How do I remove elements at a set of indices in a vector in MATLAB? 1 answer In R, I can do the following: v <- 11:20 v[-(4:5)] and get 11 12 13 16 17 18 19 20 , thus all indices except the 4th and 5th. Is there an equivalent in Matlab's indexing logic? However I wrap my mind around it, I do not seem to get the correct search terms to google my own result for this fairly elementary question. Note: Of course I might use some of the set functions, e.g. v = 11:20; v(setdiff(1:length(v), 4:5)) However, this just is not intuitive. An alternative is to

Let's say we have a vector: b = [3, 2, 1]; Let's say we also have matrix like this: A = ones([10 10 10]); I want to use vector b as a source of coordinates to assign values to matrix A . In this example it will be equivalent to: A(3, 2, 1) = 5; Is there an easy way in MALTAB to use a vector as a source of coordinates for indexing a matrix? wakjah You can do this by converting your vector b into a cell array: B = num2cell(b); A(B{:}) = 5; The second line will expand B into a comma-separated list , passing each element of B as a separate array index. Generalization If b contains coordinates for

This question already has an answer here: Create a zero-filled 2D array with ones at positions indexed by a vector 4 answers I have a vector v of size (m,1) whose elements are integers picked from 1:n. I want to create a matrix M of size (m,n) whose elements M(i,j) are 1 if v(i) = j, and are 0 otherwise. I do not want to use loops, and would like to implement this as a simple vector-matrix manipulation only. So I thought first, to create a matrix with repeated elements M = v * ones(1,n) % this is a (m,n) matrix of repeated v For example v=[1,1,3,2]' m = 4 and n = 3 M = 1 1 1 1 1 1 3 3 3 2 2 2

For example I have A=[11 24 33 47 52 67] and I have indices matrix as I = [2 3] so I want to have the elements of A from the indices other than indices given with I. So I want to have B = [11 47 52 67] . How can I do it and use I as a negated indices matrix? go for idx = logical(ones(size(A))); % // all indices here or, as @Gunther Struyf suggests, idx = true(size(A)); then idx(I) = 0; % // excluding not desired indices B = A(idx); % // selection Alternatively B = A; B(I) = []; You can also make use of setdiff to exclude indices. Here's a one-liner for you: B = A(setdiff(1:numel(A), I)) 来源：

I'd like to perform metrics on the contents of an array that do NOT fall within certain ranges. For example, I have an array with 1000 rows and 2 columns. I'd like to perform a mean() calculation on all the elements in one column (let's say column #2) that don't fall in rows 50-150, 250-300, 400-700 and 900-950. Thus, the mean should be calculated based on rows 1-49, 151-249, 301-399, 701-899 and 951-1000. Any ideas how to go about this? Edit: I should point out that those items which are included will change each time the program is run. Therefore, I can't just hard-code the inclusions in;