[R] Deleting certain observations (and their imprint?)

[PIKAL Petr]

Hi

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Stodola, Kirk
> Sent: Thursday, November 29, 2012 5:32 PM
> To: r-help at r-project.org
> Subject: [R] Deleting certain observations (and their imprint?)
> 
> I'm manipulating a large dataset and need to eliminate some
> observations based on specific identifiers.  This isn't a problem in
> and of itself (using which.. or subset..) but an imprint of the deleted
> observations seem to remain, even though they have 0 observations.
> This is causing me problems later on.  I'll use the dataset warpbreaks
> to illustrate, I apologize if this isn't in the best format
> 
> ##Summary of warpbreaks suggests three tension levels (H, M, L)
> > summary(warpbreaks)
> 
>      breaks      wool   tension
>  Min.   :10.00   A:27   L:18
>  1st Qu.:18.25   B:27   M:18
>  Median :26.00          H:18
>  Mean   :28.15
>  3rd Qu.:34.00
>  Max.   :70.00
> 
> ## Subset the dataset and keep only those observations with "L"
> > wb.subset <- warpbreaks[which(warpbreaks$tension=="L"),]

wb.subset <- warpbreaks[which(warpbreaks$tension=="L"), , drop=TRUE]
or
warpbreaks$tension <-  factor(warpbreaks$tension)
or
change tension from factor to character vector.

Regards
Petr



> 
> 
> ##Summary of the subsetted data shows: L=18, M=0, H=0, Why is M and H
> still included?
> > summary(wb.subset)
> 
>      breaks      wool  tension
>  Min.   :14.00   A:9   L:18
>  1st Qu.:26.00   B:9   M: 0
>  Median :29.50         H: 0
>  Mean   :36.39
>  3rd Qu.:49.25
>  Max.   :70.00
> 
> ##The subsetted dataset does not show M or H
> > wb.subset
> 
> Is there a way that M & H can be completely eliminated (i.e. they don't
> show up in summary)? The only way I found was to export the dataset and
> then reimport, which seems pretty cumbersome.  Thanks in advance for
> any help.  -Kirk
> 
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