r - Finding rows containing a value (or values) in any column

Question

Say we have a table 'data' containing Strings in several columns. We want to find the indices of all rows that contain a certain value, or better yet, one of several values. The column, however, is unknown.

What I do, at the moment, is:

apply(df, 2, function(x) which(x == "M017"))

where df =

1 04.10.2009 01:24:51   M017  <NA>  <NA>    NA
2 04.10.2009 01:24:53   M018  <NA>  <NA>    NA
3 04.10.2009 01:24:54   M051  <NA>  <NA>    NA
4 04.10.2009 01:25:06   <NA>  M016  <NA>    NA
5 04.10.2009 01:25:07   <NA>  M015  <NA>    NA
6 04.10.2009 01:26:07   <NA>  M017  <NA>    NA
7 04.10.2009 01:26:27   <NA>  M017  <NA>    NA
8 04.10.2009 01:27:23   <NA>  M017  <NA>    NA
9 04.10.2009 01:27:30   <NA>  M017  <NA>    NA
10 04.10.2009 01:27:32   M017  <NA>  <NA>    NA
11 04.10.2009 01:27:34   M051  <NA>  <NA>    NA

This also works if we try to find more than one value:

apply(df, 2, function(x) which(x %in% c("M017", "M018")))

The result being:

$`1`
integer(0)

$`2`
[1]  1  2 20

$`3`
[1] 16 17 18 19

$`4`
integer(0)

$`5`
integer(0)

However, processing the resulting list of lists is rather tedious.

Is there a more efficient way to find rows that contain a value (or more) in ANY column?

Answer 1

How about

apply(df, 1, function(r) any(r %in% c("M017", "M018")))

The ith element will be TRUE if the ith row contains one of the values, and FALSE otherwise. Or, if you want just the row numbers, enclose the above statement in which(...).