[R] subset exact values

[Charles C. Berry]

On Thu, 22 Jan 2009, tsippel wrote:

>
> Hi-
> I need to subset the following data by the column 'dal' for values that
> equal the regular interval seq(0, 150, by=0.5) exactly....
>
> ....excluding rows with irregular 'dal' values such as  c(2.888958,
> 2.891620), etc.
>
> data<-data.frame(id=id, dal=dal, date=date, mu.x=mu.x)
>
> $dal
> [1] 0.000000 0.500000 1.000000 1.500000 2.000000 2.500000 2.888958 2.891620
> 3.000000 3.245405 3.500000 3.688333 4.000000 4.500000 4.738831 4.855949
> [17] 4.993437 5.000000 5.251875 5.252037 5.500000
>
> $id
> [1] STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3
> STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3 STM05.3
> [19] STM05.3 STM05.3 STM08.2
>
> $date
> [1] "2005-02-26 00:00:00" "2005-02-26 12:00:00" "2005-02-27 00:00:00"
> "2005-02-27 12:00:00" "2005-02-28 00:00:00" "2005-02-28 12:00:00"
> [7] "2005-02-28 21:20:06" "2005-02-28 21:23:56" "2005-03-01 00:00:00"
> "2005-03-01 05:53:23" "2005-03-01 12:00:00" "2005-03-01 16:31:12"
> [13] "2005-03-02 00:00:00" "2005-03-02 12:00:00" "2005-03-02 17:43:55"
> "2005-03-02 20:32:34" "2005-03-02 23:50:33" "2005-03-03 00:00:00"
> [19] "2005-03-03 06:02:42" "2005-03-03 06:02:56" "2005-03-03 12:00:00"
>
> $mu.x
> [1] 176.2730 176.3550 176.4996 176.6969 176.9209 177.1511 177.3197 177.3197
> 177.3109 177.2958 177.5862 177.7929 177.7612 177.6563 177.6030 177.6421
> [17] 177.6932 177.6949 177.7377 177.7377 177.7468
>
> Why does the following subset code give me rows of data with irregular 'dal'
> values which do not exactly match values in 'seq' below?
>
> seq<-seq(0, 150, 0.5)
> reg<-subset(data, dal=seq, select=c(id, dal, date, mu.x))


Same reason that this doesn't return only those rows where V2 is 1:

> dat <- as.data.frame(diag(2))
> subset(dat,V2=1)
   V1 V2
1  1  0
2  0  1
>

which I suspect is a typo or a misunderstanding of what '=' means.

Have a look at the manuals.

While you are there look at FAQ 7.31 'Why doesn't R think these numbers 
are equal?' to be sure you don't get tripped up by that issue.

HTH,

Chuck


>
> Thanks,
>
> Tim
>
> -- 
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>
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>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901