how to calculate number of unique element in array?

Hi all.

if I have matrix like:

c =

1 1

1 1

1 1

2 1

2 2

2 3

2 4

2 5

2 5

3 1

3 1

3 2

how can I calculate number of unique element in column 2 according to column 1?

for the above matrix, the result should be:

1 1

2 5

3 2

Thanks in advance

Answer 1

[Ameer Hamza]

Try splitapply()

c = [
     1     1
     1     1
     1     1
     2     1
     2     2
     2     3
     2     4
     2     5
     2     5
     3     1
     3     1
     3     2]
 
out = [unique(c(:,1)) ...
     splitapply(@(x) numel(unique(x)), c(:,2), c(:,1))]

or accumarray():

out = [unique(c(:,1)) ...
     accumarray(c(:,1), c(:,2), [], @(x) numel(unique(x)))];

And if the second column also contain all positive integers in increasing order then you can just try

out = [unique(c(:,1)) ...
     splitapply(@max, c(:,2), c(:,1))]
%
out = [unique(c(:,1)) ...
     accumarray(c(:,1), c(:,2), [], @max)];

[Putri Basenda Tarigan]

Thankyou so much, it helps a lot

Answer 2

[Bruno Luong]

c =[
    1     1
    1     1
    1     1
    2     1
    2     2
    2     3
    2     4
    2     5
    2     5
    3     1
    3     1
    3     2 ]

d=unique(c,'rows');
c1=d(:,1);
i=find([true; diff(c1)~=0; true]);
count=diff(i);
c1=c1(i(1:end-1));
t=table(c1,count)