R: Convert characters to numeric in data.frame with unknown column classes

Question

There is a nice discussion of how to convert character into numerics in this SO here. Maybe I missed something in that post, but what would one do if one does not know which columns are "convertable" (if any) ? Is it possible to check for convertability ? In addition, I usually suppress factor conversion (like character better) - so characters should be characters (not factors).

df <- data.frame(a=as.character(c(NA, 1/3)), b=letters[1:2], c=c('1|2', '4|2'), d=as.character(3:4), stringsAsFactors = F)

Then apply ... some function f ... to get:

str(f(df))
'data.frame':   2 obs. of  4 variables:
 $ a: num  NA 0.333
 $ b: chr  "a" "b"
 $ c: chr  "1|2" "4|2"
 $ d: int  3 4

How to achieve this for any data.frame not known beforehand ?

jay.sf · Accepted Answer · 2018-06-15T12:14:57.257

2

You could do something like this (not very elegant though).

fun1 <- function(i) {
  if (!all(is.na(as.numeric(df[, i])))){
    as.numeric(df[, i])
  } else {
    df[, i]
  }
}

df1 <- "names<-"(cbind.data.frame(lapply(seq_along(df), fun1),
                                  stringsAsFactors=FALSE), names(df))

> str(df1)
'data.frame':   2 obs. of  4 variables:
 $ a: num  NA 0.333
 $ b: chr  "a" "b"
 $ c: chr  "1|2" "4|2"
 $ d: num  3 4

Or more generally:

convertiblesToNumeric <- function(x){
  x2 <- cbind.data.frame(lapply(seq_along(x), function(i) {
    if (!all(is.na(as.numeric(x[, i])))){
      as.numeric(x[, i])
      } else {
        x[, i]
        }
    }), stringsAsFactors=FALSE)
  names(x2) <- names(x)
  return(x2)
}

df1 <- convertiblesToNumeric(df)
> str(df1)
'data.frame':   2 obs. of  4 variables:
 $ a: num  NA 0.333
 $ b: chr  "a" "b"
 $ c: chr  "1|2" "4|2"
 $ d: num  3 4

edited Jun 15 '18 at 12:14

answered Jun 15 '18 at 11:08

jay.sf

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But works. What is happening with the "names – user3375672 Jun 15 '18 at 11:34
You could also do `df1 – jay.sf Jun 15 '18 at 11:37
1

Try `?"names – jay.sf Jun 15 '18 at 11:45
1

Perhaps your function - for completeness - should allow a second parameter for `df` when ones data.frame is named something different (than `df`). As in `fun1 – user3375672 Jun 15 '18 at 11:55
Cool. And even put `as.character( x[, i])` inside `as.numeric( ... )` both places in case you get a factor (otherwise you convert the levels). – user3375672 Jun 15 '18 at 12:18
1

That would not work as expected. Better is to transform all to character with `df[] – jay.sf Jun 15 '18 at 12:42

R: Convert characters to numeric in data.frame with unknown column classes

1 Answers1