class - Change all columns from factor to numeric in R

Question

I am working with a big dataset that is causing some trouble because some of the columns I the dataset are being treated as factors. How can I convert all of the columns from factor to numeric, without having to do that column by column??

I have tried to apply a small loop, but it returns NA values. Here's a sample data that applies to the case:

data <- structure(list(v1 = c(22.394, 43.72, 58.544, 56.877, 1.659, 29.142, 
67.836, 68.851), v2 = c(144.373, 72.3, 119.418, 112.429, 35.779, 
41.661, 166.941, 126.548), v3 = structure(c(33L, 29L, 33L, 5L, 
13L, 31L, 5L, 8L), .Label = c("", "#VALUE!", "0", "1", "10", 
"11", "12", "13", "14", "15", "16", "17", "18", "19", "2", "20", 
"21", "22", "23", "24", "25", "26", "28", "29", "3", "30", "32", 
"33", "4", "48", "5", "6", "7", "8", "9"), class = "factor"), 
    v4 = structure(c(24L, 6L, 22L, 23L, 16L, 22L, 23L, 26L), .Label = c("", 
    "-1", "-2", "-4", "#VALUE!", "0", "1", "10", "11", "12", 
    "13", "14", "15", "16", "17", "18", "19", "2", "24", "28", 
    "29", "3", "4", "5", "6", "7", "8", "9"), class = "factor")), .Names = c("v1", 
"v2", "v3", "v4"), row.names = c("4", "5", "6", "7", "8", "9", 
"10", "11"), class = "data.frame")

for (i in 1:ncol(data)){
data[,i] <- as.numeric(as.character(data[i]))
} ## returns NAs

Is there some command that I can apply to turn all these columns into a numeric class?

Answer 1

This works but I'm thinking your data has an odd character or space, something that makes it read in as factor. You can try reading in with the argument stringsAsFactors = FALSE. But still wouldn't address character vs numeric read in. Here's a fix:

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

## > str(data)
## 'data.frame':   8 obs. of  4 variables:
##  $ v1: num  22.39 43.72 58.54 56.88 1.66 ...
##  $ v2: num  144.4 72.3 119.4 112.4 35.8 ...
##  $ v3: num  7 4 7 10 18 5 10 13
##  $ v4: num  5 0 3 4 18 3 4 7