Subset data.frame by column

Question

I have this data.frame:

a <- c(rep(\"1\", 3), rep(\"2\", 3), rep(\"3\",3), rep(\"4\",3), rep(\"5\",3))
b <- c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15)
df <-         


        

Answer 1

We can use data.table. We convert the 'data.frame' to 'data.table' (setDT(df)), and set the 'key' as column 'a', then we subset the rows.

library(data.table)
setDT(df, key= 'a')[c('2','3')]
#   a b
#1: 2 4
#2: 2 5
#3: 2 6
#4: 3 7
#5: 3 8
#6: 3 9

Answer 2

what about this?

library(dplyr)
df %>% filter(a == 2 | a==3)
  a b
1 2 4
2 2 5
3 2 6
4 3 7
5 3 8
6 3 9

Answer 3

You're confusing == with %in%:

subset(df, a %in% c(2,3))
#   a b
# 4 2 4
# 5 2 5
# 6 2 6
# 7 3 7
# 8 3 8
# 9 3 9