Convert Factors in 2 Data Frames of a List into Numeric

Question

I am having trouble converting the columns of 2 data frames in a list to numeric. Right now both data frames have 2 columns consisting of factors. I want to convert them to numeric so that I can do mathematical operations on them. Below is sample code:

library(XML)

bal <- "http://www.baseball-reference.com/teams/BAL/2014-schedule-scores.shtml"
bos <- "http://www.baseball-reference.com/teams/BOS/2014-schedule-scores.shtml"

mylist <- list(bal, bos)

a <- lapply(mylist, readHTMLTable)
b <- lapply(a, function(x) x[["team_schedule"]][, c("R", "RA")])
c <- as.numeric(as.character(b))

When I run this code I get:

> c
[1] NA NA
> str(c)
 num [1:2] NA NA

Here is the structure of b:

> str(b)
List of 2
 $ :'data.frame':   165 obs. of  2 variables:
  ..$ R : Factor w/ 13 levels "","0","10","11",..: 6 6 7 8 10 7 6 5 9 2 ...
  ..$ RA: Factor w/ 13 levels "","0","1","10",..: 3 9 7 4 10 3 7 8 7 6 ...
 $ :'data.frame':   166 obs. of  2 variables:
  ..$ R : Factor w/ 10 levels "","0","1","2",..: 3 8 6 4 8 2 7 9 6 3 ...
  ..$ RA: Factor w/ 13 levels "","1","10","14",..: 5 5 6 9 10 7 2 3 5 7 ...

What should I do differently to convert the factors into numeric values?

Answer 1

You need to use lapply. do a str on "b"

str(b)

This will let you know you have a list of 2 of 2 data.frames.

So you need to use lapply along with sapply, to preserve the data structure

lapply(b, function(x) sapply(x, function(x) as.numeric(as.character(x))))

You have D/N in your factor, which will be converted to NAs and also the list entries that are blank/empty