Histogram of different classes of variables in one column
This isn't a bioinformatics question, but it's quicker to answer than to close.

df1 &lt;- read.table(text = "
AA 4
AA 6
BB 6
AB 5
BA 4
AA 3
NN 2
AN 6
NN 5
AN 4
NA 3
BB 6
BN 5
NB 1
BN 7", na.strings = "")

library(ggplot2)

ggplot(df1, aes(x = V1, y = V2)) +
  geom_bar(stat = "identity")