Using for loop for arrays

I have an array that includes a list of temps, and I am trying to count the temps less than 75. This is the code I used -

clc;
clear;
close all;
count=0;
a = [45, 56, 66, 78, 54, 67, 56, 88, 95, 93, 23, 56, 78, 45, 67, 56, 34, 67, 87, 64, 94, 57, 61, 24];   %16 below 75
for i = 1 : length(a)
    if i < 75
        count = count+1;
    end 
end
disp(count)

Not sure what is wrong. I am not able to get the desired output. Any help?

Answer 1

[Guillaume]

Not sure what is wrong

You'll always going to get min(74, numel(a)) as a count, since you're comparing the index i instead of the value a(i) to 75.

Note that as usual in matlab, there's no need for a loop for this

count = nnz(A < 75)
%or
count = sum(A < 75)

[Archit Muchhal]

Thank you. I tried the similar approach for other values. But that doesn't seem to work the same way.

clc;
clear workspace;
close all;
count = 0; 
count2 = 0; 
count3 = 0; 
count4 =0;
a = [45, 56, 66, 78, 54, 67, 56, 88, 95, 93, 23, 56, 78, 45, 67, 56, 34, 67, 87, 64, 94, 57, 61, 24, 96, 98, 100, 109];

count = sum(a<75)
count2 = sum(75<a<95)
count3 = sum(95<a<105)
count4 = sum(a>105)

The variables "count2" and "count3" return output as 28, which is the array size. How do I rectify it?

[Guillaume]

Well, yes, if you look at any matlab code (or for that matter code in other languages), they never use the syntax low<x<high. That's because it doesn't do what you want.

low < x < high first compares low to x and returns a logical vector of 0 and 1. it then compares this logical vector of 0 and 1 to high. So if high is greater than 1 the final result is just a vector of 1. Just as you get. The proper syntax is low < x & x < high.

So

count2 = sum(75<a & a<95);
%etc.

Note that numbered variables are universally a bad idea. Rather than embedding the index into the variable, use proper indexing:

count(1) = nnz(a < 75);
count(2) = nnz(75 < a & a < 95);  %what about if a is 75?
count(3) = nnz(95 < a & a < 105); %or 95?
count(4) = nnz(a > 105);          %or 105?

But even better, use histcounts:

count = histcounts(a, [-Inf, 75, 95, 105, Inf])