# Create a row Matrix

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Konstantinos on 12 Jan 2015
Commented: John D'Errico on 13 Jan 2015
I want to create a row matrix of 20 elements (1x20), which consists of 1s and 0s. 1s are generated with rate:r and 0s are generated with rate:(1-r), where r could be any random number between 0 and 1 ( 0<r<1 ).
Any help could be useful. Thanks in advance!
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### Accepted Answer

Star Strider on 12 Jan 2015
Edited: Star Strider on 12 Jan 2015
This is one option:
r = 0.5;
idx = randperm(20, ceil(r*20));
rv = zeros(1,20);
rv(idx) = 1;
The logic is relatively straightforward: ‘idx’ uses rendperm to generate a matrix of index positions, then generates ‘rv’ and uses ‘idx’ to determine the r*20 values that are set to 1.
With r = 0.5, this yields:
rv =
Columns 1 through 17
0 1 0 0 1 0 0 1 1 1 1 0 1 0 0 1 1
Columns 18 through 20
1 0 0
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Star Strider on 12 Jan 2015
Our pleasure!

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### More Answers (1)

John D'Errico on 12 Jan 2015
Edited: John D'Errico on 12 Jan 2015
Well, since a test returns a 0 or 1 (i.e., true or false) what is the probability that each element of a set of random samples, taken by the call rand(1,20), is greater than r? What is the probability that they are less than r?
x = (rand(1,20) >= r);
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John D'Errico on 13 Jan 2015
Star - Oh, I don't dispute that you may arguably have a valid answer of the question. Questions are frequently slightly ambiguous, so they can often be read many ways. My patience today is clearly stressed by probabilistically meaningless statements like this:
"if r = 0.37, then the number of ones I want is: N1 = ceil(r*20)=8 1s and No=(1 - N1)=12 0s"

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