[R] problem subsetting data frame with variable instead of constant

[vaneet]

Hello,

I've encountered a very weird issue with the method subset(), or maybe this
is something I don't know about said method that when you're subsetting
based on the columns of a data frame you can only use constants (0.1, 2.3,
2.2) instead of variables?

Here's a look at my data frame called 'ea.cad.pwr':
*>ea.ca.pwr[1:5,]
   MAF   OR  POWER
1 0.02 0.01 0.9999
2 0.02 0.02 0.9998
3 0.02 0.03 0.9997
4 0.02 0.04 0.9995
5 0.02 0.05 0.9993*

Here's my subset lines which finds no rows:

*power1 = subset(ea.cad.pwr, MAF == maf1 & OR == odds)
power2 = subset(ea.cad.pwr, MAF == maf2 & OR == odds)
*
Now when maf1 = 0.2 and odds = 1.2 it finds nothing.  I know for a fact that
there's a row with these values:
*> ea.cad.pwr[1430:1432,]
     MAF   OR  POWER
1430 0.2 0.58 0.9996
1431 0.2 1.20 0.3092
1432 0.2 1.22 0.3914*

I have code working in a loop and each previous iteration the subset()
function is working fine, but in this iteration some different lines are
executed which are relevant to these variables, here they are:
*
maf1 = maf.adj - 0.01
maf2 = maf.adj + 0.01*

Basically maf.adj is always a 2 decimal number (in this case = 0.21), and
I'm computing the numbers around it by a difference of 0.01 (0.2,0.22) in
case maf.adj isn't in the table.  maf.adj is read from another dataframe,
when I use it to subset it always works fine but when I do this innocent
subtraction for some reason it doesn't work.  If I rewrite statements like
this it works:

*power1 = subset(ea.cad.pwr, MAF == 0.2 & OR == odds)
power2 = subset(ea.cad.pwr, MAF == 0.22 & OR == odds)
*

Even if I write this first:

maf1 = 0.2

Then:

power1 = subset(ea.cad.pwr, MAF == maf1 & OR == odds)

It works as well! That's what's really confusing, how can this subtraction
mess everything up?  Please help if you can..thank you!

Vaneet

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