Counting frequencies of each letter for multiple column [duplicate]

Answer 1

We can use sapply to loop over the columns, convert it to factor with levels specified and get the frequency with table

sapply(dfnew, function(x) table(factor(x, levels = c("A", "C", "G", "T"))))

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Or using tidyverse

library(dplyr)
library(tidyr)
dfnew %>% 
    gather(key, val, na.rm = TRUE) %>% 
    count(key, val) %>% 
    spread(key, n)