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

One approach is to use a combination of dplyr and tidyr to convert data into long format, and do the computation:

library(dplyr)
library(tidyr)
df %>%
  gather(key, value, -ID) %>%
  group_by(ID) %>%
  summarise(numtwos = sum(value == 2)) %>%
  inner_join(df, .)

Output is as follows:

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