[R] Question on matrix calculation
Christofer Bogaso
bogaso.christofer at gmail.com
Thu Jan 24 20:39:05 CET 2013
Hello again,
Ley say I have 1 matrix and 1 data frame:
> mat <- matrix(1:15, 5)
> match_df <- data.frame(Seq = 1:5, criteria = sample(letters[1:5], 5, replace = T))
> mat
[,1] [,2] [,3]
[1,] 1 6 11
[2,] 2 7 12
[3,] 3 8 13
[4,] 4 9 14
[5,] 5 10 15
> match_df
Seq criteria
1 1 c
2 2 e
3 3 c
4 4 c
5 5 d
Now I want to get the column-sums of 'mat' based on the unique
elements of match_df[,'criteria']
Therefore based on the 'match_df', my resulting matrix will have 3
rows (because the unique elements here are 'c, e, & d'). And.........
1st row will be column sums for mat[c(1,3,4), ]
2nd row will be column sums for mat[c(2), ]
3rd row will be column sums for mat[c(5), ]
I want to get a general framework, so that I can implement that in
some big arbitrary matrix.
Can somebody give me some pointer?
Thanks and regards,
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