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   sw  1   io
GGG   e   90  gv
CCC   r   34  scf
CCC   t   21  fvb
KOO   y   45  hffd
EEE   u   2   asd
LLL   i   4   dlm
ZZZ   i   8   zzas

I would like to collapse the first column and add the corresponding PSM values and I would like to get the following output:

ID  Sum PSM
ABC 2
CCC 58
DDD 56
EEE 80
FFF 1
GGG 90
KOO 45
LLL 4
ZZZ 8

It seems doable with aggregate function but don't know the syntax. Any help is really appreciated! Thanks.

Answer 1

Using data.table

setDT(df1)[,  lapply(.SD, sum) , by = ID, .SDcols = "PSM" ]

Answer 2

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.

Answer 3

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

Answer 4

This is super easy using the plyr package:

library(plyr)
ddply(df1, .(ID), summarize, Sum=sum(PSM))