# Creating 1D array from frequency data/histogram?

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Rose Lakatos on 15 Jun 2018
Answered: Steven Lord on 27 Jun 2018
I’m trying to run an algorithm that requires a 1 dimensional data to work. My data is grey values from ct images describing the frequency of 8bit pixel values from 0-255. Is it possible to create an 1D array [0,1,2,3,4,5...255] with corresponding frequency of that pixel value?

Steven Lord on 27 Jun 2018
If you want the resulting array to contain exactly n(1) copies of x(1), n(2) copies of x(2), etc. use the repelem function. [Depending on how you want to use the result, you may also want to "shuffle" it using randperm.]
x = 0:5;
freq = [2 3 4 5 6 7];
A = repelem(x, freq);
If instead of frequencies you have probabilities for what each element of the resulting array should be, use discretize.
p = freq./sum(freq);
cumulativeprob = [0 cumsum(p)];
B = discretize(rand(1, 1000), cumulativeprob, x);
Let's check that the proportions of elements in B come close to the probabilities in p.
c = histcounts(B, 'BinEdges', [x x(end)], 'Normalization', 'probability');
[c; p]
The values in c look reasonably close to the probabilities in p for just 1000 samples.

Gayatri Menon on 27 Jun 2018
Hi,
Could you check out "histogram" command. Please refer to the below documentation to know more on this comment:
Hope this helps.
Gayatri

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