How to count no of iterations of first digit.

I want to count number of times first digit of first column is repeating. If

a = [11 3;
     12 4;
     13 3;
     21 2;
     22 5;
     23 6;
     24 3];

So, I want to get result in form of 1 = 3 and 2 = 4

[the cyclist]

Is that column guaranteed to be two-digit numbers, or could it be

a = [ 11 3;
     121 4]

?

[Vishal Sharma]

Two digits only

Answer 1

[Stephen23]

Assuming that there are always two digits:

>> a = [11 3;
        12 4;
        13 3;
        21 2;
        22 5;
        23 6;
        24 3]
>> tmp = fix(a(:,1)/10);
>> uni = unique(tmp);
>> cnt = histc(tmp,uni)
cnt =
3
4
>> [uni,cnt]
ans =
 1   3
 2   4

Answer 2

[the cyclist]

a = [11 3;
     12 4;
     13 3;
     21 2;
     22 5;
     23 6;
     243 3];

a1 = a(:,1);

firstDigits = floor(a1./(10.^floor(log10(a1))));

uniqueFirstDigit = unique(firstDigits);

firstDigitCount = histcounts(firstDigits,[uniqueFirstDigit; Inf])'