将新列添加到数据框列表

Question

I'm cleaning up some data I'm importing from excel, from a large number of files, and have to create two keys based on subscript from the file name during the import. The files are imported by country. I managed to import the files into separate data frames, but ran into difficulties creating the new variables. For brevity, I have set country="usa" and year=1980.

My first thought was to create a list of the data frames present in the environment, by filtering for the pattern "USA". However, this is poor style, and the product seems to be a character list which is not connected to the data frames themselves.

usadflist <- Filter(is.data.frame, mget(ls(pattern="USA")))

This is when I turned to adjusting the actual import, using dplyr::mutate(), however could not specify a variable that hasn't been created yet, which is when I tried cbind(), as follows:

usalist <- list.files(path ="~/Desktop/reports/usa")

for(i in usalist) {
  assign(paste(i),read_excel(path = paste("Desktop/reports/usa/",i,sep="")))
  cbind(usalist[[i]][country]<-"usa", usalist[[i]][year]<-1980)
}

An error message is given: Error in *tmp* [[i]] : subscript out of bounds .

What I am expecting is that each of the data frames will have a new variable: country, with the value "usa" & a variable: year, with the value 1980. Any help would be greatly appreciated.

Answer 1

Have you tried something like:

usalist <- list.files(path ="~/Desktop/reports/usa")

for(i in 1:length(usalist)){
  df <- read_excel(path = paste("Desktop/reports/usa/", usalist[i], sep = ""))
  df$country <- "usa"
  df$year <- 1980L
  assign(usalist[i], df); rm(df)
}; rm(i)

Haven't run it so I can't say whether I haven't slipped a typo in by mistake.