using data.table and its pipe worflow with [:
library(data.table)
tab <- fread("
C1 C2 C3 C4 C5 C6
A A G A G A
A T T T G G
T A G A T A
C A A A A G
C A T T T C
C A A A T A
T C T G A A
G A G C T A
C T A T G A
G A A A G G
G G T T T A
G A C T T A
T T C T T T
A T A G C T
A C A A A A
A A C A A A
T G G A A T
A A A A G T
G T G G NA NA")
tab[, melt(.SD, measure.vars = paste0("C", 1:6), na.rm = TRUE)][
, dcast(.SD, value ~ variable, fun = length, drop = TRUE)
]
#> value C1 C2 C3 C4 C5 C6
#> 1: A 6 10 7 9 5 10
#> 2: C 4 2 3 1 1 1
#> 3: G 5 2 5 3 5 3
#> 4: T 4 5 4 6 7 4
