R help - Apr 2011 - Removing row with smallest value, for a given factor

I have a table.
First column is a date, second column is an index and other columns contains
some other values.
I want to remove, for each date, the row with the smallest index (it is not
necessarily 1).

ex: in the following table, I want to remove row 1 (2013-05-12 with index 2) and
row 8 (2013-05-13 with index 1)

? ? ? ? ? ?day index values
1 ? ?2013-05-12 ? ?2 ?xxxx
2 ? ?2013-05-12 ? ?3 ?xxxx
3 ? ?2013-05-12 ? ?4 ?xxxx
4 ? ?2013-05-12 ? ?5 ?xxxx
5 ? ?2013-05-12 ? ?6 ?xxxx
6 ? ?2013-05-12 ? ?7 ?xxxx
7 ? ?2013-05-12 ? ?8 ?xxxx
8 ? ?2013-05-13 ? ?1 ?xxxx
9 ? ?2013-05-13 ? ?3 ?xxxx
10 ? 2013-05-13 ? ?4 ?xxxx
11 ? 2013-05-13 ? ?5 ?xxxx
12 ? 2013-05-13 ? ?6 ?xxxx
13 ? 2013-05-13 ? ?7 ?xxxx
14 ? 2013-05-13 ? ?8 ?xxxx
15 ? 2013-05-13 ? ?9 ?xxxx
16 ? 2013-05-13 ? 10 ?xxxx
17 ? 2013-05-13 ? 12 ?xxxx


Thank you for your help

On Apr 23, 2011, at 9:05 AM, - - wrote:
> I have a table.
> First column is a date, second column is an index and other columns  
> contains some other values.
> I want to remove, for each date, the row with the smallest index (it  
> is not necessarily 1).
>
> ex: in the following table, I want to remove row 1 (2013-05-12 with  
> index 2) and row 8 (2013-05-13 with index 1)
>
>            day index values
> 1    2013-05-12    2  xxxx
> 2    2013-05-12    3  xxxx
> 3    2013-05-12    4  xxxx
> 4    2013-05-12    5  xxxx
> 5    2013-05-12    6  xxxx
> 6    2013-05-12    7  xxxx
> 7    2013-05-12    8  xxxx
> 8    2013-05-13    1  xxxx
> 9    2013-05-13    3  xxxx
> 10   2013-05-13    4  xxxx
> 11   2013-05-13    5  xxxx
> 12   2013-05-13    6  xxxx
> 13   2013-05-13    7  xxxx
> 14   2013-05-13    8  xxxx
> 15   2013-05-13    9  xxxx
> 16   2013-05-13   10  xxxx
> 17   2013-05-13   12  xxxx
>
Consider using ave and creating a logical vector that you then negate:

 > ave(dat$index, list(dat$day), FUN=function(x) x==min(x))
  [1] 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0

dat[ -ave(dat$index, list(dat$day), FUN=function(x) x==min(x)), ]


--

David Winsemius, MD
West Hartford, CT