How can I change the name of a data frame

Question

I have a recurrent situation where I set a value at the top of a long set of R code that\'s used in subsetting one or more data frames. Something like this:

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Answer 1

Generally, you shouldn't be programmatically generating names for data frames in your global environment. This is a good indication that you should be using list to make your life simpler. See the FAQ How to make a list of data frames? for many examples and more discussion.

Using your concrete example, I would rewrite it in one of a few different ways.

library(dplyr)
gear_code <- 4
gear_subset <- paste("mtcars_", gear_code, sep = "")
mtcars_subset <- mtcars %>% filter(gear == gear_code)
head(mtcars_subset)
write.csv(mtcars_subset, file = paste(gear_subset, ".csv", sep = ""))

The goal seems to be to write a CSV called gear_X.csv that has the mtcars subset with gear == X. You don't to keep an intermediate data frame around, this should be fine:

gear_code <- 4
mtcars %>% filter(gear == gear_code) %>%
    write.csv(file = paste0('mtcars_', gear_code, '.csv'))

But probably you're coding it this way because you want to do it for each value of gear, and this is where dplyr's group_by helps:

CSVs for all the gears

mtcars %>% group_by(gear) %>%
  do(csv = write.csv(file = sprintf("mt_gear_%s.csv", .[1, "gear"]), x = .)

Data frames for each gear level:

If you really want individual data frame objects for each gear level, keeping them in a list is the way to go.

gear_df = split(mtcars, mtcars$gear)

This gives you a list of three data frames, one for each level of gear. And they are named with the levels already, so to see the data frame with all the gear == 4 rows, do

gear_df[["4"]]

Generally, this easier to work with than three data frames floating around. Anything you want to do to all of the data frames you can do at the same time with a single lapply, and even if you want to use a for loop it's simpler than eval(parse()) or get().