How can I generate values randomly from another existing vecor?

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Mira le 2021-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/814470-how-can-i-generate-values-randomly-from-another-existing-vecor

评论： Steven Lord 2021-4-27

Hi everyone My problem is I want to generate a vector of values from other vector with zeros For example My vector is v1=[122,34,20,5,21] The new vector that I want to get is like that: V2=[122,0,20,0,0,5]

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Answer 1

J. Alex Lee 2021-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/814470-how-can-i-generate-values-randomly-from-another-existing-vecor#answer_685905

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how about

v1 = [122,34,20,5,21]
v1a = [0,v1]
N = numel(v1a)
ridx = randi(N,size(v1))
v2 = v1a(ridx)

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J. Alex Lee 2021-4-27

how does it fail?

Steven Lord 2021-4-27

在 MATLAB Online 中打开

Looking at the error message you posted in your other message I suspect your v1 vector is actually a column vector, not a row vector.

v1 = [1, 2, 3]
v1 = 1×3
     1     2     3
v1a = [0, v1]
v1a = 1×4
     0     1     2     3
v2 = [1; 2; 3]
v2 = 3×1
     1
     2
     3
v2a = [0; v2]
v2a = 4×1
     0
     1
     2
     3
v2bWILLNOTWORK = [0, v2]
Error using horzcat
Dimensions of arrays being concatenated are not consistent.

In v2bWILLNOTWORK, 0 has 1 row and v2 has 3 rows. You can't put them side-by-side in a vector but you can stack them on top of one another as shown with v2a. Compare with v1a, where both 0 and v1 had 1 row and so could be stored side-by-side.

If I'd written v1a with [0; v1] that wouldn't have worked since 0 and v1 don't have the same number of columns.

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