How to convert certain columns only to numeric?

Question

How can I convert certain columns only in a data frame to numeric?

For instance, I have this data frame:

structure(list(airport = c(         


        

Answer 1

The all.is.numeric function from the Hmisc package does a good job determining whether a given column can be cast to numeric.

Using this, you could do:

numeric_cols <- sapply(weatherDF, Hmisc::all.is.numeric)

if (sum(numeric_cols) > 1)  {
    weatherDF[,numeric_cols] <- data.matrix(weatherDF[,numeric_cols])
} else {
    weatherDF[,numeric_cols] <- as.numeric(weatherDF[,numeric_cols])
}

Answer 2

num.cols <- c('ws','wd','humidity')
weatherDF[num.cols] <- sapply(weatherDF[num.cols], as.numeric)

Answer 3

Using dplyr:

library(dplyr)
df %>% 
  mutate_at(vars(ws, wd, humidity), as.numeric)

# A tibble: 2 x 5
airport xdate         ws    wd humidity
  <chr>   <chr>      <dbl> <dbl>    <dbl>
1 EGLL    2016-07-28    6.  237.      68.
2 EGLL    2016-07-31    5.  299.      55.

Answer 4

1) All your columns is character columns <- sapply(weatherDF, is.character)

airport    xdate       ws       wd humidity 
    TRUE     TRUE     TRUE     TRUE     TRUE

2) Why not simply ?

weatherDF[, 3:ncol(weatherDF)] <- lapply(3:ncol(weatherDF), function(x) as.numeric(weatherDF[[x]]))

or

columns <-c("ws", "wd", "humidity")
weatherDF[, columns] <- lapply(columns, function(x) as.numeric(weatherDF[[x]]))

If your dont know which columns is numeric you can try to find it using tryCatch like

weatherDF[,1:ncol(weatherDF)]=lapply(1:ncol(weatherDF),function(x) {
  tryCatch({
    as.numeric(weatherDF[[x]])
    },warning = function(w) {
    weatherDF[[x]]}
        )} )