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07000
来自reshape2的dcast没有公式，没有重复。拿这些示例数据：
df <- structure(list(id = c("A","B","C","A","C"),cat = c("SS","SS","SV","SV"),val = c(220L,222L,223L,224L,225L,2206L)),.Names = c("id","cat","val"),class = "data.frame",row.names = c(NA,-6L))
我想dcast这些数据，只是将值列表，而不对value.var应用任何函数，包括默认长度。
在这种情况下，它工作正常。
> dcast(df,id~cat,value.var="val") id SS SV 1 A 220 224 2 B 222 225 3 C 223 2206
但是当有重复的变量时，乐趣默认为长度。有办法避免吗？
df2 <- structure(list(id = c("A",220L,1L)),-7L))
> dcast(df2,value.var="val")
Aggregation function missing: defaulting to length
id SS SV
1 A 1 1
2 B 1 1
3 C 1 2
理想情况下，我正在寻找的是添加一个fun = NA，因为不要尝试聚合value.var。 df2中我想要的结果df2：
id SS SV 1 A 220 224 2 B 222 225 3 C 223 220 4. C NA 1
我不认为有办法直接做，但我们可以添加一个额外的列，这将有助于我们
df2 <- structure(list(id = c("A",-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
