Can dcast be used without an aggregate function?
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This R reshaping should be simple, but
dcast from reshape2 works without a formula where there are no duplicates. Take these example data:
df <- structure(list(id = c("A", "B", "C", "A", "B", "C"), cat = c("SS",
"SS", "SS", "SV", "SV", "SV"), val = c(220L, 222L, 223L, 224L,
225L, 2206L)), .Names = c("id", "cat", "val"), class = "data.frame", row.names = c(NA,
-6L))
I'd like to dcast these data and just have the values tabulated, without applying any function to the value.var including the default length.
In this case, it works fine.
> dcast(df, id~cat, value.var="val")
id SS SV
1 A 220 224
2 B 222 225
3 C 223 2206
But when there are duplicate variables, the fun defaults to length. Is there a way to avoid it?
df2 <- structure(list(id = c("A", "B", "C", "A", "B", "C", "C"), cat = c("SS",
"SS", "SS", "SV", "SV", "SV", "SV"), val = c(220L, 222L, 223L,
224L, 225L, 220L, 1L)), .Names = c("id", "cat", "val"), class = "data.frame", row.names = c(NA,
-7L))
> dcast(df2, id~cat, value.var="val")
Aggregation function missing: defaulting to length
id SS SV
1 A 1 1
2 B 1 1
3 C 1 2
Ideally what I'm looking for is to add a fun = NA, as in don't try to aggregate the value.var. The result I'd like when dcasting df2:
id SS SV
1 A 220 224
2 B 222 225
3 C 223 220
4. C NA 1
Answer
I don't think there is a way to do it directly but we can add in an additional column which will help us out
df2 <- structure(list(id = c("A", "B", "C", "A", "B", "C", "C"), cat = c("SS",
"SS", "SS", "SV", "SV", "SV", "SV"), val = c(220L, 222L, 223L,
224L, 225L, 220L, 1L)), .Names = c("id", "cat", "val"), class = "data.frame", row.names = c(NA,
-7L))
library(reshape2)
library(plyr)
# Add a variable for how many times the id*cat combination has occured
tmp <- ddply(df2, .(id, cat), transform, newid = paste(id, seq_along(cat)))
# Aggregate using this newid and toss in the id so we don't lose it
out <- dcast(tmp, id + newid ~ cat, value.var = "val")
# Remove newid if we want
out <- out[,-which(colnames(out) == "newid")]
> out
# id SS SV
#1 A 220 224
#2 B 222 225
#3 C 223 220
#4 C NA 1