Convert all columns to characters in a data.frame

问题

Consider a data.frame with a mix of data types.

For a weird purpose, a user needs to convert all columns to characters. How is it best done? A tidyverse attempt at solution is this:

map(mtcars,as.character) %>% map_df(as.list) %>% View()
c2<-map(mtcars,as.character) %>% map_df(as.list)

when I call str(c2) it should say a tibble or data.frame with all characters.

The other option would be some parameter settings for write.csv() or in write_csv() to achieve the same thing in the resulting file output.

回答1:

You can also use dplyr::mutate_all.

library(dplyr)
mtcars %>%
  mutate_all(as.character)

回答2:

mutate_all and re-casting the data.frame after lapply will cause the data.frame's attributes to change. If you need to retain row.names, labels or other attributes associated with the underlying data.frame, try:

x[] <- lapply(x, as.character)

This converts the columns to character class in place, retaining the data.frame's attributes.

Example

x <- mtcars
attr(x, "example") <- "1"

Only in the last case below is the example attribute retained:

x %>%
  mutate_all(as.character) %>%
  attributes()

data.frame(lapply(x, as.character)) %>%
  attributes()

x[] <- lapply(x, as.character)
attributes(x)

回答3:

This might work, but not sure if it's the best.

df = data.frame(lapply(mtcars, as.character))
str(df)

回答4:

Most efficient way using data.table-

data.table::setDT(mtcars)
mtcars[, (colnames(mtcars)) := lapply(.SD, as.character), .SDcols = colnames(mtcars)]

Note: You can use this to convert few columns of a data table to your desired column type.

If we want to convert all columns to character then we can also do something like this-

to_col_type <- function(col_names,type){
            get(paste0("as.", type))(dt[[col_names]])
            }
mtcars<- rbindlist(list(Map(to_col_type ,colnames(mtcars),"character")))

来源：https://stackoverflow.com/questions/43789278/convert-all-columns-to-characters-in-a-data-frame

标签

dataframe

tidyverse