Hi,
I have a data-frame r (shown below is a subset) with the following column
names:
date    time    sample    vct    norm    hct    deltact

$time has 8 levels: 0h, 0.5h, .....24h. $deltact holds real numbers.
I want to subset this dataframe by the levels of $time.  For all the rows
which have r$time == "0h" I would like to convert the present value of
r$deltact to 0.
Any pointers to a simple method to accomplish would be greatly appreciated.

TIA,
Anjan


-- 
===================================
anjan purkayastha, phd.
research associate
fas center for systems biology,
harvard university
52 oxford street
cambridge ma
phone-703.740.6939
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