Retaining variables in dcast in R

Question

I am using the dcast function in R to turn a long-format dataset into a wide-format dataset. I have an ID number, a categorical variable (CAT

Answer 1

I added some extra data lines to clarify some parts of this. But the gist is that you just need to put SEX on the left hand side (i.e., of ~):

PC2 <- read.table(text="ID CAT AMT SEX 
1  A   46  Female 
1  B   22  Female 
1  C   31  Female 
2  A   17  Male 
2  B   25  Male 
2  C   44  Male
3  A   47  Female 
3  B   27  Female 
3  C   37  Female 
4  A   17  Male 
4  A   17  Male 
4  B   22  Male 
4  B   NA  Male 
4  C   44  Male", header=T)

library(reshape2)
PC1cast2 <- dcast(PC2, ID+SEX~CAT, value.var='AMT', fun.aggregate=sum, 
                  na.rm=TRUE)
PC1cast2
#   ID    SEX  A  B  C
# 1  1 Female 46 22 31
# 2  2   Male 17 25 44
# 3  3 Female 47 27 37
# 4  4   Male 34 22 44

In your example data, you only have one instance of each combination and no NAs, so the fun.aggregate=sum, na.rm=TRUE doesn't do anything. When some are duplicated (e.g., there are two 4 As and two 4 Bs), the values are summed, but the NAs are dropped first. Make sure that is what you want.