Hello

I wish to extract the row indices from a data.frame in which a column contains numeric data by calculating the minimum value, but grouped on another column factor:

An example data.frame:

Code                absdiff
NY14/3070         2
NY14/3070         4
NY14/3070         1
NY14/5459         5
NY14/5459         7

So in this case the factor is Code and the numeric vector is absdiff

The query would return row indices 3 and 4 which have the minimum values for the factor.
I am sure it would involve some combination of which and tapply but cannot figure it out?

Many thanks, Barry

Dr Barry Rawlins
British Geological Survey
Keyworth
Nottingham
NG12 5GG
UK
Tel: 0115 9363140
Mob: 07884235473
homepage http://sites.google.com/site/barryrawlins/



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