R help - Mar 2010 - removing fields of the same group from a data frame

Dear all,

I'm trying to find a a way to remove certain fields belonging to the same
group from a data frame structure.

I have a data frame like this:

 foo v1 v2 v3
       1  1  a
       6  2  a
       3  8  a
       4  4  b
       4  4  b
       2  1  c
       1  6  d

Each row can then be grouped according to the third column: a, b, c, d. Then
I would like to remove all fields that belong to a group with less than X
members, for example less than 3 members, then
the resulting data frame structure would look like:


 foo v1 v2 v3
       1  1   a
       6  2   a
       3  8   a

Is there some simple way to do this in R?

Thanks in advance.
/Oscar

	[[alternative HTML version deleted]]

Try this:

subset(foo, v3 %in% names(which(!table(foo$v3) < 3)))

On Wed, Mar 24, 2010 at 10:38 AM, Oscar Franz?n
<oscar.franzen2 at gmail.com> wrote:
> Dear all,
>
> I'm trying to find a a way to remove certain fields belonging to the
same
> group from a data frame structure.
>
> I have a data frame like this:
>
> ?foo v1 v2 v3
> ? ? ? 1 ?1 ?a
> ? ? ? 6 ?2 ?a
> ? ? ? 3 ?8 ?a
> ? ? ? 4 ?4 ?b
> ? ? ? 4 ?4 ?b
> ? ? ? 2 ?1 ?c
> ? ? ? 1 ?6 ?d
>
> Each row can then be grouped according to the third column: a, b, c, d.
Then
> I would like to remove all fields that belong to a group with less than X
> members, for example less than 3 members, then
> the resulting data frame structure would look like:
>
>
> ?foo v1 v2 v3
> ? ? ? 1 ?1 ? a
> ? ? ? 6 ?2 ? a
> ? ? ? 3 ?8 ? a
>
> Is there some simple way to do this in R?
>
> Thanks in advance.
> /Oscar
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paran?-Brasil
25? 25' 40" S 49? 16' 22" O

On Mar 24, 2010, at 8:38 AM, Oscar Franz?n wrote:
> Dear all,
> 
> I'm trying to find a a way to remove certain fields belonging to the
same
> group from a data frame structure.
> 
> I have a data frame like this:
> 
> foo v1 v2 v3
>       1  1  a
>       6  2  a
>       3  8  a
>       4  4  b
>       4  4  b
>       2  1  c
>       1  6  d
> 
> Each row can then be grouped according to the third column: a, b, c, d.
Then
> I would like to remove all fields that belong to a group with less than X
> members, for example less than 3 members, then
> the resulting data frame structure would look like:
> 
> 
> foo v1 v2 v3
>       1  1   a
>       6  2   a
>       3  8   a
> 
> Is there some simple way to do this in R?
> 
> Thanks in advance.
> /Oscar
> DF
  v1 v2 v3
1  1  1  a
2  6  2  a
3  3  8  a
4  4  4  b
5  4  4  b
6  2  1  c
7  1  6  d
> subset(DF, !v3 %in% names(which(table(v3) < 3)))
  v1 v2 v3
1  1  1  a
2  6  2  a
3  3  8  a


The use of table() gets us:
> table(DF$v3) < 3
    a     b     c     d 
FALSE  TRUE  TRUE  TRUE 

followed by:
> names(which(table(DF$v3) < 3))
[1] "b" "c" "d"

which gives us the values of v3 that don't have at least 3 entries.

When using subset(), the variables are evaluated first within the data frame,
hence we can drop the 'DF$' in the function call. The use of
"%in%" in subset() allows us to include or exclude certain values from
a set comparison.

We could also reverse the logic, yielding the same result:
> subset(DF, v3 %in% names(which(table(v3) >= 3)))
  v1 v2 v3
1  1  1  a
2  6  2  a
3  3  8  a


See ?table, ?subset and ?"%in%" for more information.

HTH,

Marc Schwartz