How to count the frequency of a string for each row in R

Question

I have a .txt file that looks something like this:

rs1 NC AB NC     
rs2 AB NC AA  
rs3 NC NC NC  
...  

For each row, I would like to coun

Answer 1

df$count <- rowSums(df[-1] == "NC")
#    V1 V2 V3 V4 count
# 1 rs1 NC AB NC     2
# 2 rs2 AB NC AA     1
# 3 rs3 NC NC NC     3

We can use rowSums on the matrix that is created from this expression df[-1] == "NC".