Create new variables based on list, then populate based on whether row contains variable name

Question

I have some data:

df = data.frame(matrix(rnorm(20), nrow=10))
         X1          X2
1   1.17596402  0.06138821
2  -1.76439330  1.03674803
3  -0.39069424  0.61616793
4   0.68375346  0.27435354
5   0.27426476 -1.71226109
6  -0.06153577  1.14514453
7  -0.37067621 -0.61243104
8   1.11107852  0.47788971
9  -1.73036658  0.31545148
10 -1.83155718 -0.14433432

I want to add new variables to it for every element in a list, which changes:

list = c("a","b","c")

The result should be:

           X1          X2  a  b  c
1   1.17596402  0.06138821 NA NA NA
2  -1.76439330  1.03674803 NA NA NA
3  -0.39069424  0.61616793 NA NA NA
4   0.68375346  0.27435354 NA NA NA
5   0.27426476 -1.71226109 NA NA NA
6  -0.06153577  1.14514453 NA NA NA
7  -0.37067621 -0.61243104 NA NA NA
8   1.11107852  0.47788971 NA NA NA
9  -1.73036658  0.31545148 NA NA NA
10 -1.83155718 -0.14433432 NA NA NA

I can do this using suggestions below:

df[list] <- NA

But now, I want to search every row for the variable name as a value and flag if it contains that value. For example:

   X1 X2 a b c
1   a  b 1 1 0
2   a  c 1 0 1

So the code would search for "a" in all columns and flag if any column contains "a". How do I do this?

Answer 1

You can use

df[list] <- NA

The result:

            X1          X2  a  b  c
1  -2.07205164 -0.93585363 NA NA NA
2   1.11014587  0.23468072 NA NA NA
3  -1.17909665  0.04741478 NA NA NA
4   0.23955056  1.02029880 NA NA NA
5  -0.79212220 -1.13485661 NA NA NA
6  -0.57571547  0.33069641 NA NA NA
7  -0.70063920 -0.17251563 NA NA NA
8   1.90625189  0.30277177 NA NA NA
9   0.09029121 -0.72104778 NA NA NA
10 -1.36324313 -1.48041873 NA NA NA

If you want to add only the variables that are not present in df, you can use:

df[list[!list %in% names(df)]] <- NA