[R] For loop with ifelse help

[Steve Lianoglou]

Hi Pele,

On Wed, Sep 22, 2010 at 12:40 PM, Pele <drdionc at yahoo.com> wrote:
>
> Hi David - thanks for your suggestion, but I am trying to avoid doing any
> merging and sorting for this step because the real file I will be working
> with has about 20 million records.  If I can get this loop  or something
> similar to work will be good enough.

If that's the case, you might consider looking at the sqldf or
data.table packages.

They both implement data.frame-like objects, but can do subsetting
(and merging) rather quickly since they implement indexes over "keys"
(columns) of the respective data.frame(s).

Subsetting "normal" data.frames in this scenario you describe involves
a linear search for every query through the column(s) you are querying
against, which can get slow as the size of your data.frames get large.

-steve

-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact