Apply common function to all data frames and return data frames with same name

Question

I'm trying to apply a function to all similarly spelled data frames in my global environment in R. I want to apply this function to all these data frames, but I can't figure out how to do it without me specifying 1 by 1. I want to return the data frame to the global environment with the same spelling as it was before.

mtcars_test = mtcars
iris_test = iris
#....etc......could be 2 of them or 88 of them...but they will all end in "_test"

# figure out what data frames I am working with
list_of_my_dfs = lapply(ls(pattern = "*_test"), get)

#my function just multiples everything by 2
mytest_function = function(df){ df = df*2; return(df)}

helpme_return_these_dfs_to_outside_the_list=plyr::llply(list_of_my_dfs, mytest_function)

This is where I need help. I want to apply my function to each data frame within the list AND then 'return' the data frame from that list to my environment. So mtcars_test and all other data frames will be multiplied by 2 everywhere and returned back to global environment.

I can keep it in a list but the for purpose I'm in right now I need them extracted. I already know how to do that and think I'm doing that right now. — runningbirds
The "answer" is probably list2env, but please don't bother with that. Just keep them in a list. — joran

G. Grothendieck G. Grothendieck · Accepted Answer · 2016-09-15T22:28:15

1) environment subscripting Set e to the environment containing the data frames and then get their names and loop over them as shown:

BOD_test <- BOD  # not all columns of iris are numeric so use BOD instead
mtcars_test <- mtcars

e <- .GlobalEnv
nms <- ls(pattern = "_test$", envir = e)
for(nm in nms) e[[nm]] <- mytest_function(e[[nm]])

1a) assign An alternative to the last statement would be:

for(nm in nms) assign(nm, mytest_function( get(nm, e) ), e)

2) lists You might want, instead, to keep the data frames in a list:

L <- sapply(nms, get, envir = e, simplify = FALSE)
L[] <- lapply(L, mytest_function)

2a) sapply or if you do not want to overwrite L then:

sapply(L, mytest_function, simplify = FALSE)

Apply common function to all data frames and return data frames with same name

2 Answers