[R] extracting rows from dataframe that match a vector

[Karin Lagesen]

Hi!

I have a large dataframe that I want to extract a subset from. This
subset has a certain column value that matches elements in a vector I
have defined. So, my question is how do I get the rows that match one
of the elements in the vector.

Example:

a = c(1:5)
b = letters[1:10]
df = data.frame(ind = a, letrs = b)

> df
   ind letrs
1    1     a
2    2     b
3    3     c
4    4     d
5    5     e
6    1     f
7    2     g
8    3     h
9    4     i
10   5     j
>


# Now I want to extract all of the rows where ind == 2, 4 or 5.
# This would be rows 2, 4, 5, 7, 9 and 10 

subgr = c(2,4,6)

My most natural inclination would be to do 

df[df$ind == subgr,]

However, this does not work:


> df[df$ind == subgr,]
  ind letrs
7   2     g
Warning message:
In df$ind == subgr :
  longer object length is not a multiple of shorter object length
>

So, which part of this is it that I have misunderstood?

Thanks for your help btw!

Karin
-- 
Karin Lagesen, PhD student
karin.lagesen at medisin.uio.no
http://folk.uio.no/karinlag