Data manipulation question, need some help!!

Guys, I really need some help here. I got stuck for a long time.

1. How am I supposed to create a matrix that has two columns, the format of the first one is string, and the second is numerical?

Say a = ['1';'2';'3'], b = [4,5,6], I need to create a matrix like c =

      1      4
      2      5
      3      6

I tried to use c = {a,b}, but the answer is c = [3x1 char] [3x1 double]

2. A =

          '15'      3854
          '10'      6331
          '10'      4324
          '20'      3874
          '25'      4321
          '15'      6835
          '10'      3321
          '15'      3821
          '20'      9324

I need to sum the 2nd column according to the 1st column and create a new matrix. E.g, for '10', I should sum up (6331,4324,3321) , the final result should be

B =

                  '10'        13976
                  '15'        10689
                  '20'        13198
                  '25'         4321

Any opinion is welcomed!

[Tom]

If the first column is always numerical, would it be easier to convert the strings to numbers, then convert back to strings when needed?

[Xiao Tang]

I think that may be a good suggestion. So far I didn't see much difference though.

Answer 1

[Andrei Bobrov]

A ={...
'15'      3854
'10'      6331
'10'      4324
'20'      3874
'25'      4321
'15'      6835
'10'      3321
'15'      3821
'20'      9324}
[a b b] =  unique(A(:,1));
out = [a num2cell(accumarray(b,cat(1,A{:,2})))];

OR

out2 = [str2double(a) accumarray(b,cat(1,A{:,2}))];

[Xiao Tang]

Thanks Andrei. It worked perfectly well!

Could you tell me what the cat(1,A{:,2}) does ? Does that convert cell array back to number?

Thanks again!

Answer 2

[Walter Roberson]

Ta = cellstr(a);
Tb = num2cell(b);
c = [Ta(:), Tb(:)];

[Xiao Tang]

Thanks for your reply! It totally solves Question 1.

Is it true that I have to convert those to columns to cell array before I can combine them?