Using lapply to apply a function over list of data frames and saving output to files with different names

Question

I have a list of data frames and have given each element in the list (e.g. each data frame) a name:

e.g.

df1 <- data.frame(x = c(1:5), y = c(11:15))   df2 <- data.frame(x = c(1:5), y = c(11:15))   mylist <- list(A = df1, B = df2)   

I have a function that I want to apply to each data frame; In this function, I want to include a line to write the results to file (eventually I want to do more complicated things like save plots of the correlation between two variables for each data frame but thought I'd start simple)

e.g.

NewVar <- function(mydata, whichVar, i) {   mydata$newVar <- mydata[, whichVar] + 1   write.csv(mydata, file = i)   } 

I want to use lapply() to apply this function to each data frame in my list

something like:

hh<-lapply(mylist, NewVar, whichVar = "y") 

I can't figure out how to assign the "i" within the context of lapply so that i iterates over the names in the list of data frames, saving multiple files with different names (in this case, two files named A and B) that correspond with the modified data frames.

Answer 1

It will work with the following lapply call:

lapply(names(mylist), function(x) NewVar(mylist[[x]], "y", x)) 

Answer 2

There are many options. For example:

  lapply(names(mylist),          function(x)write.csv(mylist[x],                               file =paste0(x,'.csv'))) 

or using indexes :

 lapply(seq_along(mylist),      function(i)write.csv(mylist[i],                           file =paste0(names(mylist)[i],'.csv')))