Retaining variables in dcast in R - 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), and a continuous variable (AMT). However, I also have a variable SEX, which is the same for all rows of a given ID number. This code works to create the wide-format dataset, but I lose SEX. How can I retain it?
PC1cast <- dcast(PC1, ID~CAT, value.var='AMT', fun.aggregate=sum, na.rm=TRUE)
If I add SEX to the ID~CAT line, it gives me SEX-CAT combinations. I want SEX to just be one value for each row.
Sample data:
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

Answer 1

For that, you need to add SEX to the ID side of your formula:
dcast(PC1, ID + SEX~CAT, value.var='AMT', fun.aggregate=sum, na.rm=TRUE)
# results in:
ID SEX A B C
1 1 Female 46 22 31
2 2 Male 17 25 44
Things on the left hand side of the formula are kept as-is, things on the right-hand side are cast.

Answer 2

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.