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Data manipulation question, need some help!!

2 次查看（过去 30 天）
Xiao Tang
Xiao Tang 2012-6-18
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!
  2 个评论
Tom
Tom 2012-6-18
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
Xiao Tang 2012-6-18
I think that may be a good suggestion. So far I didn't see much difference though.

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2012-6-18
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}))];
  1 个评论
Xiao Tang
Xiao Tang 2012-6-18
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!

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更多回答（1 个）

Walter Roberson
Walter Roberson 2012-6-18
Ta = cellstr(a);
Tb = num2cell(b);
c = [Ta(:), Tb(:)];
  1 个评论
Xiao Tang
Xiao Tang 2012-6-18
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?

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