function to loop string column to numeric in R

Question

I'm trying to convert few column of a data frame from char to numeric in R.

Exemple:

transform_function <- function(dataframe, vector){
  for (i in vector){
    dataframe[[i]] <- as.numeric(dataframe[[i]])
  }
  return(dataframe)
}

where my data frame has columns from a to z and I do this:

vector <- c("a", "c", "d", "h")

transform_function(dataframe, vector)

Getting the follow error:

Error in `[[<-.data.frame`(`*tmp*`, i, value = numeric(0)) : 
  replacement has 0 rows, data has 11068 
4.
stop(sprintf(ngettext(N, "replacement has %d row, data has %d", 
    "replacement has %d rows, data has %d"), N, nrows), domain = NA) 
3.
`[[<-.data.frame`(`*tmp*`, i, value = numeric(0)) 
2.
`[[<-`(`*tmp*`, i, value = numeric(0)) 
1.
transform_function(dataframe, vector)

Rilcon42 · Accepted Answer · 2018-02-01 20:14:48Z

1

You can use dplyr::mutate_at.

library(dplyr)
to_change <- c('a', 'c')

df <- data.frame(a = as.character(1:10), b = as.character(11:20), c = as.character(21:30))
df %>% mutate_at(to_change, as.numeric)

edited Feb 1, 2018 at 20:14

Rilcon42

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answered Feb 1, 2018 at 19:55

IceCreamToucan

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Comments

Rilcon42 · Accepted Answer · 2018-02-01 19:34:50Z

1

Try using apply to iterate over the columns rather than writing your own function. Example solution:

df <- data.frame(c("a", "c", "d", "h"),c(1,2,3,4))

df<-apply(df,2,as.numeric)
df

answered Feb 1, 2018 at 19:34

Rilcon42

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1 Comment

Onyambu Over a year ago

You know this wont work right?. eg if df <- data.frame(c("a", "c", "d", "h"),c(1,2,3,4),stringsAsFactors = F) then this code will fail

Rushabh Patel · Accepted Answer · 2018-02-01 22:05:44Z

0

Most efficient way:

 cols_to_convert <- colnames(dt)
 data.table::setDT(dt)[, (cols_to_convert) := lapply(.SD, as.numeric), .SDcols = cols_to_convert ]

answered Feb 1, 2018 at 22:05

Rushabh Patel

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