[R] Test for X=1 fails, test for >0 works, data in text file is 1

Duncan Murdoch murdoch at stats.uwo.ca
Tue Jul 7 21:23:46 CEST 2009


On 7/7/2009 3:06 PM, Mark Knecht wrote:
> Hi,
>    I am apparently not understanding some nuance about either the use
> of subset or more likely my ability to test for a numerical match
> using '='. Which is it? Thanks in advance.
> 
>    I've read a data file, reshaped it and then created MyResults by
> keeping only lines where the value column is greater than 0. So far so
> good. The data in MyResults looks good to me by eye.
> 
>    The problem comes in when I try to further subset MyResults into
> two files, one with PosType=1 and the other with PosType=-1. Looking

PosType = 1 is an assignment.  The test is PosType == 1.

Duncan Murdoch

> at the dimension of the results there's no change. It didn't work
> which is verified by eye. However if I test for PosType=1 by actually
> testing for PosType>0 then it does work.
> 
>    Is this the general case in R that if I've read data that was
> written into a csv file as 1 - it is 1 if I look into the file with a
> text editor - that I cannot test for that? Or is some case where I
> need to use maybe as.numeric or something else first to ensure R sees
> the number the way I'm thinking about the number?
> 
> Cheers,
> Mark
> 
>> dim(X)
> [1]  25 425
>>
>> ReShapeX <- melt(X, id = c("Trade", "PosType", "EnDate", "EnTime",  "ExDate",  "ExTime", "PL_Pos", "Costs", "Save2"))
>>
>> dim(ReShapeX)
> [1] 10400    11
>>
>> MyResults <- subset(ReShapeX, value > 0)
>>
>> dim(MyResults)
> [1] 1105   11
>>
>> MyResults.GroupA <- subset(MyResults, PosType = 1)
>>
>> dim(MyResults.GroupA)
> [1] 1105   11
>>
>> MyResults.GroupB <- subset(MyResults, PosType = -1)
>>
>> dim(MyResults.GroupB)
> [1] 1105   11
>>
>> MyResults.GroupA <- subset(MyResults, PosType > 0)
>>
>> dim(MyResults.GroupA)
> [1] 432  11
>>
>> MyResults.GroupB <- subset(MyResults, PosType < 0)
>>
>> dim(MyResults.GroupB)
> [1] 673  11
>>
> 
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