Histogram of different classes of variables in one column I have a basic ggplot2 R question. I have a dataframe in which data looks like this:

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


The file is of multiple lines. I want to make a histogram using gplot2 that will plot the 9 kinds of variables AA,BB,AB,BA,AN,BN,NN,NB,NA on the x-axis and the sum of it's corresponding values in the next column on the y-axis. 

So for example, here the y-values should be 

AA= 13
BB= 12
AB= 5
BA= 4
NN= 7
AN= 10
NA= 3
BN= 12
NB= 1
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")