Counting factor instance of several columns of factors

Question

I have a data frame along the lines of this:

> DF <- data.frame(V1=c("Yes", "Yes", "No"), V2=c("Yes", "No", "No"), V3=c("Yes", "Yes", "No"))
   V1  V2  V3
1 Yes Yes Yes
2 Yes  No Yes
3  No  No  No

No I would like to use something along the line of mutate to count the instances of "Yes" in each row to get something like this:

   V1  V2  V3 CountYes
1 Yes Yes Yes        3
2 Yes  No Yes        2
3  No  No  No        0

Is there an easy way to do it? I am sadly out of ideas.

Thanks and BW, Jan

Answer 1

We can use rowSums on a logical matrix

DF$CountYes <- rowSums(DF == 'Yes')
DF$CountYes
#[1] 3 2 0

Answer 2

That's an overkill, but since you've tagged this with dplyr:

library(dplyr)

DF %>%
  rowwise %>%
  mutate(CountYes = sum(c_across() == 'Yes'))

Output:

# A tibble: 3 x 4
# Rowwise: 
  V1    V2    V3    CountYes
  <fct> <fct> <fct>    <int>
1 Yes   Yes   Yes          3
2 Yes   No    Yes          2
3 No    No    No           0

Answer 3

Another base R option (but not as simple as rowSums by @akrun)

DF$CountYes <- table(stack(data.frame(t(DF))))["Yes",]

which gives

> DF
   V1  V2  V3 CountYes
1 Yes Yes Yes        3
2 Yes  No Yes        2
3  No  No  No        0