multiply columns of seperate dataframes within factor (please take a look) R

Question

v1 <- c("red", "a","b","c",1, 3, 5, 7) v2 <- c("red", "a","b","c",1, 3, 5, 7) v3 <- c("blue", "a","b","d",2, 4, 6, 8) v4 <- c("blue", "a","b","d",2, 4, 6, 8) v5 <- c("blue", "a","b","d",2, 4, 6, 8) df1 <- data.frame(rbind(v1,v2,v3,v4,v5)) v6 <- c("red", 2,2,4,2) v7 <- c("blue",1,1,0,1) df2 <- data.frame(rbind(v6,v7)) colnames(df2) <- c("Y1", "Y2", "Y3", "Y4", "Y5") > df1 X1 X2 X3 X4 X5 X6 X7 X8 v1 red a b c 1 3 5 7 v2 red a b c 1 3 5 7 v3 blue a b d 2 4 6 8 v4 blue a b d 2 4 6 8 v5 blue a b d 2 4 6 8 > df2 Y1 Y2 Y3 Y4 Y5 v6 red 2 2 4 2 v7 blue 1 1 0 1

How do I take the 4 numeric columns from df2 and multiply them within factor(red, blue) and within column (respectively)? Say I would want to take (v6, X2) and multiply it by (v1:v2,X5).

If you need further clarification of what I am trying to do please ask.

edit: For clarification, I want to make all possible multiplications of above example.

edit2: edited colnames

The fact that you have identical column names between two data frames but different variables in each will greatly complicate your problem. — Señor O
– Señor O, Commented Oct 23, 2013 at 18:10
column names are irrelevant.. use df1[,#] or change them if you want — user2795569
– user2795569, Commented Oct 23, 2013 at 18:11
No they're not, because you're going to need to merge the two data frames to do what you want efficiently. — Señor O
– Señor O, Commented Oct 23, 2013 at 18:14
Separate note, that is not how you build a data.frame. All items in v1 (and other rows) are converted to characters. You end up with a data.frame where each column is a factor... — flodel
– flodel, Commented Oct 23, 2013 at 18:19

mrip · Accepted Answer · 2013-10-23 18:30:46Z

If I understand your objective correctly, here are two possible solutions. You can use match:

> df3<-df1 > df3[,5:8]<-df3[,5:8]*df2[match(df1[,1],df2[,1]),2:5] > df3 X1 X2 X3 X4 X5 X6 X7 X8 v1 red a b c 2 6 20 14 v2 red a b c 2 6 20 14 v3 blue a b d 2 4 0 8 v4 blue a b d 2 4 0 8 v5 blue a b d 2 4 0 8

Or you can use merge:

> df3<-merge(df1,df2,by=1) > df3[,5:8]<-df3[,5:8]*df3[,9:12] > df3[,1:8] X1 X2 X3 X4 X5 X6 X7 X8 1 blue a b d 2 4 0 8 2 blue a b d 2 4 0 8 3 blue a b d 2 4 0 8 4 red a b c 2 6 20 14 5 red a b c 2 6 20 14

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