Question

Possible Duplicate:
select some values of a row in a matrix
R subset a data frame with multiple keys

Say I have a list

> test

  V1    V2   V3
1  1   one  uno
2  2   two duos
3  3 three tres
4  4 four cuatro

and a vector a<-c("one","three").

I want to get the subset of the list test where the element of the second column are from vector a.

So in this case answer should be something like,

  V1    V2   V3
1  1   one  uno
2  3 three tres

I want something on the lines of
test[test[,2]=="one",] but for multiple values. How to do that?

Answer 1

What you’re looking for is %in% (although you could also use match and subset). See below.

df <- data.frame(V1=1:4, V2=c("one", "two", "three", "four"), stringsAsFactors = FALSE)
fil <- c("one", "three")

> df
#   V1    V2
# 1  1   one
# 2  2   two
# 3  3 three
# 4  4  four

> fil
# [1] "one"   "three"

# subset df by column V2 using fil

# using %in%
df[df$V2 %in% fil, ]

# using subset
subset(df, V2 %in% fil)

# using match
df[!is.na(match(df$V2, fil)), ] # (or) 
df[which(!is.na(match(df$V2, fil))), ]

# all gives
#   V1    V2
# 1  1   one
# 3  3 three