How can I change all factor variables into numeric variables in a bulk

Question

I have a data frame that contains about 100 factorial variables that I would like to change into numeric type. How can I do it to the whole data frame? I know that I can do it per each variable by using this code for example: dat$.Var2<-as.numeric(dat$.Var2) but I would like to do it for a lot of variables. Here is an example data frame.

   dat <- read.table(text = " TargetVar  Tar_Var1    Var2       Var3
     0        0        0         7
     0        0        1         1
     0        1        0         3
     0        1        1         7
     1        0        0         5
     1        0        1         1
     1        1        0         0
     1        1        1         6
     0        0        0         8
     0        0        1         5
     1        1        1         4
     0        0        1         2
     1        0        0         9
     1        1        1         2  ", header = TRUE)

Solution

You can use lapply:

dat2 <- data.frame(lapply(dat, function(x) as.numeric(as.character(x))))

   TargetVar Tar_Var1 Var2 Var3
1          0        0    0    7
2          0        0    1    1
3          0        1    0    3
4          0        1    1    7
5          1        0    0    5
6          1        0    1    1
7          1        1    0    0
8          1        1    1    6
9          0        0    0    8
10         0        0    1    5
11         1        1    1    4
12         0        0    1    2
13         1        0    0    9
14         1        1    1    2


str(dat2)
'data.frame':   14 obs. of  4 variables:
 $ TargetVar: num  0 0 0 0 1 1 1 1 0 0 ...
 $ Tar_Var1 : num  0 0 1 1 0 0 1 1 0 0 ...
 $ Var2     : num  0 1 0 1 0 1 0 1 0 1 ...
 $ Var3     : num  7 1 3 7 5 1 0 6 8 5 ...

Comments

[mql4beginner]

Thanks Sven, It works. Can I use sapply for this task?

[alexwhan]

Just be careful using as.numeric() - see what happens with as.numeric(factor(c(7, 1))) - you might need as.numeric(as.character(x))

[Ben]

+1 @alexwhan, was going to say the same, see: stackoverflow.com/a/14717814/1036500 stackoverflow.com/a/6328860/1036500 & stackoverflow.com/a/2293313/1036500

[A5C1D2H2I1M1N2O1R2T1]

@user1024441, why do you want to use sapply for this? lapply is more appropriate. If you want to overwrite the values in dat (not create a new data.frame), you can also just use dat[] <- lapply(dat, function(x) as.numeric(as.character(x)))

[mql4beginner]

Thanks Ananda, Can you please explain why lapply is more appropriate than sapply ?

[Sven Hohenstein]

@alexwhan Good point. I modified the code accordingly.

[A5C1D2H2I1M1N2O1R2T1]

@user1024441, a data.frame is essentially a special type of list. If you use the approach I describe, you are essentially directly replacing the columns. Also, lapply is generally faster than sapply because sapply calls lapply anyway, and then checks to see whether the output can be simplified to an array (using the simplify2array function). You can do a few benchmarks to check on your own, but my quick test shows that even with this small dataset, lapply is considerably faster.