Is there a way to identify where NAs are introduced?

Question

Recently went through my fairly large dataset and realized some foo decided to use commas. Trying to convert it all to numeric. Used a nice little gsub to get rid of those pesky commas, but I'm still finding NAs introduced by coercion. Is there a way to identify the location by column and row where those NAs are being introduced so I can see why that is occurring?

Answer 1

Use the is.na() function. Consider the following data frame, which contains NA values, as an example:

> df <- data.frame(v1=c(1,2,NA,4), v2=c(NA,6,7,8), v3=c(9,NA,NA,12))
> df
  v1 v2 v3
1  1 NA  9
2  2  6 NA
3 NA  7 NA
4  4  8 12

You can use is.na along with sapply to get the following result:

> sapply(df, function(x) { c(1:length(x))[is.na(x)] })
$v1
[1] 3

$v2
[1] 1

$v3
[1] 2 3

Each column will come back along with the rows where NA values occurred.