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

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".

dat <- read.table(text="rs1 NC AB NC rs2 AB NC AA rs3 NC NC NC")
dat <- rbind(dat, dat, dat, dat)

You can use a rowwise table to get the frequencies per row In this case for row 1 to 4 the frequencies that are equal as i copied the data

freq <- apply(dat, 1, table)
    1 2 3 4 # row-number
AA  1 1 1 1
AB  2 2 2 2
NC  6 6 6 6
rs1 1 1 1 1
rs2 1 1 1 1
rs3 1 1 1 1

If you want to have aggregated frequencies over all rows use

rowSums(freq)
AA  AB  NC rs1 rs2 rs3 
 4   8  24   4   4   4

Related