Merge several data.frames into one data.frame with a loop

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You may want to look at the closely related question on stackoverflow.

I would approach this in two steps: import all the data (with plyr), then merge it together:

filenames <- list.files(path=".../tempDataFolder/", full.names=TRUE)
library(plyr)
import.list <- llply(filenames, read.csv)

That will give you a list of all the files that you now need to merge together. There are many ways to do this, but here’s one approach (with Reduce):

data <- Reduce(function(x, y) merge(x, y, all=T, 
    by=c("COUNTRYNAME", "COUNTRYCODE", "Year")), import.list, accumulate=F)

Alternatively, you can do this with the reshape package if you aren’t comfortable with Reduce:

library(reshape)
data <- merge_recurse(import.list)

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