R: How to create matrix in a loop using cast-function?

Question

I try to make a yearly country import matrix out of a yearly list using the cast function in the reshape-package. As I try this for a single year everything works fine. See code (test-dataset below!) :

OCTC2011 <- cast(OC ~ TC, data =Import_Year[["2011"]], value = "Value")

The result is a matrix containing the import-values of the year 2011 from the origin-country (OC) (rows) to the target-country (TC) (columns).

However, as I use a large dataset consisting of different products for different years, I want to put this procedure in a loop. I tried following:

library(reshape)
OCTC <- 0
for(i in 1:length(unique(Import_Year))) 
{
  OCTC[i] <- cast(OC ~ TC, data =Import_Year[[i]], value = "Value")
}

Which delivers the warning: number of items to replace is not a multiple of replacement length, probably due to a wrong indexing as I'am hardly familiar with loops.

Here I produced a simple dataset for my problem:

OC <- c("A", "A", "B", "B", "C", "C", "D", "D")
TC <- c("Z", "Z", "Y", "Y", "X", "X", "W", "W")
Value <- c(1,2,3,4,5,6,7,8)
Year <- c(2010,2011)
df_import <- data.frame(OC,TC,Value, Year)
Import_Year <- split(df_import, df_import$Year)

I appreciate every comment on this. Thanks

I'm guessing you'll need the `rehape2` package here instead of `reshape`, then `dcast` instead of `cast` and finally `value.var` instead of `value`. — David Arenburg, Sep 24 '15 at 11:28
So what didn't work exactly? It seems like the exact same thing worked in the answer below. — David Arenburg, Sep 24 '15 at 11:57
after trying your idea, I get the 2nd answer and using list() instead of 0 let it work, even as you mentioned with the reshape2-package. thanks — N.Varela, Sep 25 '15 at 18:35

score 2 · Accepted Answer · answered Sep 24 '15 at 11:33

As @DavidArenburg comments you should probably use the dcast function from the reshape2 package using the value.var argument.

Apart from that the loop should be something like this in order to work:

library(reshape2)
OCTC <- list()
for(i in 1:length(unique(Import_Year))) 
{
  OCTC[[length(OCTC)+1]] <- dcast(OC ~ TC, data =Import_Year[[i]], value.var = "Value")
}

So, you initiate a list using list() (and not a variable with the value of zero) and then you add each dcast as an element to that list.

Output:

> OCTC
[[1]]
  OC  W  X  Y  Z
1  A NA NA NA  1
2  B NA NA  3 NA
3  C NA  5 NA NA
4  D  7 NA NA NA

[[2]]
  OC  W  X  Y  Z
1  A NA NA NA  2
2  B NA NA  4 NA
3  C NA  6 NA NA
4  D  8 NA NA NA

@N.Varela Cool! Glad I could help :) – LyzandeR Sep 24 '15 at 11:41 — LyzandeR, Sep 24 '15 at 11:41

R: How to create matrix in a loop using cast-function?

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