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

In base:

aggregate(PSM ~ ID, data=x, FUN=sum)
##    ID PSM
## 1 ABC   2
## 2 CCC  58
## 3 DDD  56
## 4 EEE  80
## 5 FFF   1
## 6 GGG  90
## 7 KOO  45
## 8 LLL   4
## 9 ZZZ   8