adding values in certain columns of a data frame in R

Question

I'm new to R. In a data frame, I wanted to create a new column #21 that is equal to the sum of column #1 to #20,row by row.

I knew I could do

df$Col21<-df$Col1+df$Col2+.....+df$Col20

But is there a more concise expression?

Also, can I achieve this if using column names not numbers? Thanks!

martin · Accepted Answer · 2014-08-13 18:08:19Z

3

There is rowSums:

df$Col21 = rowSums(df[,1:20])

should do the trick, and with names:

df$Col21 = rowSums(df[,paste("Col", 1:20, sep="")])

With leading zeros and 3 digits, try:

df$Col21 = rowSums(df[,sprintf("Col%03d", 1:20, sep="")])

edited Aug 13, 2014 at 18:08

answered Aug 11, 2014 at 19:21

martin

3,2591 gold badge29 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

A5C1D2H2I1M1N2O1R2T1 Over a year ago

+1. For interactive use subset would also work: rowSums(subset(df, select = Col1:Col20)).

lukeA · Accepted Answer · 2014-08-11 20:57:39Z

0

I find the dplyr functions for column selection very intuitive, like starts_with(), ends_with(), contains(), matches() and num_range():

df <- as.data.frame(replicate(20, runif(10)))
names(df) <- paste0("Col", 1:20)
library(dplyr)
# e.g.
summarise_each(df, funs(sum), starts_with("Col")) 
# or
rowSums(select(df, contains("8")))

answered Aug 11, 2014 at 20:57

lukeA

54.4k5 gold badges102 silver badges102 bronze badges

Collectives™ on Stack Overflow

adding values in certain columns of a data frame in R

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related