Question on matrix calculation

Hi,

You could also use:
mat <- matrix(1:15, 5)
set.seed(5)
match_df <- data.frame(Seq = 1:5, criteria = sample(letters[1:5], 5, replace = T),stringsAsFactors=F)
library(plyr) 
res<-daply(as.data.frame(mat),.(match_df$criteria),colSums)
res 
???????????????? 
#match_df$criteria V1 V2 V3
? # ???????????? a? 5 10 15
?? # ??????????? b? 5 15 25
??? # ?????????? d? 2? 7 12
????? # ???????? e? 3? 8 13


A.K.



----- Original Message -----
From: Christofer Bogaso <bogaso.christofer at gmail.com>
To: r-help <r-help at r-project.org>
Cc: 
Sent: Thursday, January 24, 2013 2:39 PM
Subject: [R] Question on matrix calculation

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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