Count number of values in row using dplyr

Question

This question should have a simple, elegant solution but I can\'t figure it out, so here it goes:

Let\'s say I have the following dataset and I want to count the num

Answer 1

Just wanted to add to the answer of @evan.oman in case you only want to sum rows for specific columns, not all of them. You can use the regular select and/or select_helpers functions. In this example, we don't want to include X1 in rowSums:

df %>% 
  mutate(numtwos = rowSums(select(., -X1) == 2))

  ID X1 X2 X3 numtwos
1  A  2  5  2       1
2  B  2  5  1       0
3  C  3  4  4       0
4  D  5  4  2       1
5  E  2  1  4       0