R- Collapse rows and sum the values in the column

Question

I have the following dataframe (df1):

ID    someText    PSM OtherValues
ABC   c   2   qwe
CCC   v   3   wer
DDD   b   56  ert
EEE   m   78  yu
FFF           


        

Answer 1

Example using dplyr, the next iteration of plyr:

df2 <- df1 %>% group_by(ID) %>%
     summarize(Sum_PSM = sum(PSM))

When you put the characters %>%, you are "piping." This means you're inputting what is on the left side of that pipe operator and performing the function on the right.