Changing Classes in Multiple Data Frames

Question

is there a better way to change the class of these dataframes and columns than repeating this? Thanks!

 df46$`Measurement Date` <- as.Date(df46$`Measurement Date`, format = "%Y-%m-%d")
 df45$`Measurement Date` <- as.Date(df45$`Measurement Date`, format = "%Y-%m-%d")
 df44$`Measurement Date` <- as.Date(df44$`Measurement Date`, format = "%Y-%m-%d")
 df43$`Measurement Date` <- as.Date(df43$`Measurement Date`, format = "%Y-%m-%d")
 df42$`Measurement Date` <- as.Date(df42$`Measurement Date`, format = "%Y-%m-%d")
 df41$`Measurement Date` <- as.Date(df41$`Measurement Date`, format = "%Y-%m-%d")
 df40$`Measurement Date` <- as.Date(df40$`Measurement Date`, format = "%Y-%m-%d")

Would using the lapply function make more sense?

 lapply(df46:df40[`Measurement Date`], Date)

If the data.frames are of similar structure, consider putting them into a list. [This post](http://stackoverflow.com/questions/17499013/how-do-i-make-a-list-of-data-frames) would be worth a read. gregor's answer there gives a number of tips on working with lists of data.frames. My answer provides a fairly simple way to get similarly names data.frames into a list. — lmo, Mar 27 '17 at 19:22
you could use lapply to do the job. But you would get a list of data.frames. They might be difficult to work with. May I ask why do you have that many data.frames in the first place? — DJJ, Mar 27 '17 at 19:23
@DJJ Each data frame is approx 250MB files and there are about 25 files. R is not letting me change the combined dataframe classes for some reason, so I have to scrub each file individually before combining. — Starbucks, Mar 27 '17 at 19:28

score 4 · Accepted Answer · edited Mar 27 '17 at 19:38

4

You can try with eval parse:

for (i in 40:46){
  eval(parse(text =
  paste0('df',i,'$`Measurement Date` <-
         as.Date(df',i,'$`Measurement Date`, format = "%Y-%m-%d")')
  ))
}

edited Mar 27 '17 at 19:38

Nick Kennedy

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answered Mar 27 '17 at 19:29

Vasilis Vasileiou

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Nice answer. Possibly more readable would be to use `eval(substitute())` e.g. ``eval(substitute(df$`Measurement Date` <- as.Date(df$`Measurement Date`, format = "%Y-%m-%d"), list(df = as.name(paste0("df", i)))))`` – Nick Kennedy Mar 27 '17 at 19:40

Changing Classes in Multiple Data Frames

1 Answers1