Extracting the data from a column vector according to mod

I have a column vector x. I want to create a vector x1 that are the 1st, 5th, 9th, ... elements of x, x2 that are the 2nd, 6th, 10th elements of x, etc. Please advise how to write a concise code for this task.

Answer 1

[KL]

Instead of creating multiple variables, why not simply reshape your vector into a matrix?

 x = (1:20);
 reshape(x,4,[])
 ans =
     1     5     9    13    17
     2     6    10    14    18
     3     7    11    15    19
     4     8    12    16    20

Answer 2

[Basil Saeed]

Given x, you can do:

x1 = x(1:4:length(x))
x2 = x(2:4:length(x))
...

Even more concisely, if you want to extra x1 ... x4, you can do:

for i=1:4
    eval(['x' num2str(i) '=x(i:4:length(x))'])
end

Answer 3

[Geoff Hayes]

alphedhuez - you could use arrayfun to return a cell array of each of the columns that are parsed (from *x) as per your instructions. For example, suppose

 x = (1:100)';

Then we can create your new arrays that are subsets of x as follows

 Z = arrayfun(@(k)x(k:4:length(x)), 1:length(x), 'UniformOutput', false);

@(k)x(k:4:50), is an anonymous function that (in this case) takes as input a scalar that we will use to extract data from x starting at index k and then using a step size of four will extract all other data from indices k+4, k+8, ..., 100 (the length of x).

The second input parameter to arrayfun is our k - the starting indices that we wish to extract data from x.

Z{1} will be your column of data extracted from indices 1,5,9,... Z{2} will be your column of data extracted from indices 2,6,10,... etc.