# Finding frequency of values in an array

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Ahmad Alenezi on 23 Jul 2019
Commented: Dyuman Joshi on 26 Jul 2023
Hi there
I have a 128x128x16 double array. Firstly, I would like to get the total number of values < zero in this array. Then, i would like to get the sum of the frequency of occurance of each value in this array. The array name is Phase.
thanks

Star Strider on 23 Jul 2019
One approach:
negPhase = nnz(Phase < 0); % Number Of Values < 0
[uPhase,ia,ic] = unique(Phase);
tally = accumarray(ic, 1);
freqOccurrence = [uPhase, tally]; % Frequency Of Occurrenct Of Each Value
If you do not want the results sorted (since the unique function does this by default), use:
[uPhase,ia,ic] = unique(Phase, 'stable');
instead. The rest of the code is unchanged. (Note that this will conform to the MATLAB linear matrix indexing convention, so it will be a column vector, not a matrix.)
Leyla Elyasizad on 26 Jul 2023
Hey Guys
Thanks for your helpful comments but I tried both unique & tabulate for double values with 4 decimal places (0.0202, 0.0031,.....) and with both functions I get two 0.0031 with differenct occurence!
Do you have any idea why this happens?
Dyuman Joshi on 26 Jul 2023
@Leyla Elyasizad, because both numbers do not appear to be the same. See below -
%Assign 0.3
y = 0.3
y = 0.3000
%Value st
sprintf('%0.42f', y)
ans = '0.299999999999999988897769753748434595763683'
When trying to compare floating point numbers, it is better to use a tolerance.
y = 0.12230455
y = 0.1223
sprintf('%0.42f', y)
ans = '0.122304549999999997988986422114976448938251'
%Set tolerance of 10^-6
tol = 1e-6;
%%Comparison
%Using equality
isequal(y,0.12330455)
ans = logical
0
%Using a tolerance
abs(y-0.12230455)<tol
ans = logical
1
With the same idea in mind, try uniquetol instead of unique

dipanka tanu on 1 May 2020
can you use tabulate operator of matlab ?
Star Strider on 1 May 2020
Try it!