Apply a function to all the elements of a data frame

问题

I am trying to apply some transformations to all the elements in a dataframe.

When using the regular apply functions, I get a matrix back and not a dataframe. Is there a way to get a dataframe directly without adding as.data.frame to each line?

df = data.frame(a = LETTERS[1:5], b = LETTERS[6:10])

apply(df, 1, tolower) #Matrix
apply(df, 2, tolower) #Matrix
sapply(df, tolower)   #Matrix

as.data.frame(sapply(df, tolower)) # Can I avoid "as.data.frame"?

回答1:

We can use lapply and assign it back to 'df'

df[] <- lapply(df, tolower)

The [] preserves the same structure as the original dataset. Using apply convert it to a matrix and that is not recommended.

回答2:

Here's a way using dplyr:

library(dplyr)
df  %>% mutate_each(funs(tolower))

来源：https://stackoverflow.com/questions/40278906/apply-a-function-to-all-the-elements-of-a-data-frame