MATLAB Answers

Extracting the data from a column vector according to mod

19 views (last 30 days)
alpedhuez
alpedhuez on 5 Jun 2018
Answered: KL on 5 Jun 2018
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.

Answers (3)

KL
KL on 5 Jun 2018
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

Basil Saeed
Basil Saeed on 5 Jun 2018
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

Geoff Hayes
Geoff Hayes on 5 Jun 2018
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.

Products

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!