Question

Suppose I have a dataframe ‘H’, like so

C1  C2  
a   1
b   1
c   2
d   3
e   4
f   4
g   5

and a list X (as.factor) that goes

"1" "2" "4"

Using the match command,

X2=H[match(X,H$C2),] 

only reduces H to three rows and only one instance of each element of X is present (a,c,e). What command should I employ to reduce H to X such that all instances of elements found in X are present (i.e, the reduced table should contain a,b,c,e,f)?

Cheers.

Answer 1

> H[H$C2 %in% X,]
  C1 C2
1  a  1
2  b  1
3  c  2
5  e  4
6  f  4