I understand your explanation about the test for even numbers. However I am
still a bit confused as to how to go about finding a particular value. Here
is an example data set
col # attr1 attr2 attr 3 LON LAT
17209 D NA NA -122.9409 38.27645
17210 BC NA NA -122.9581 38.36304
17211 B NA NA -123.6851 41.67121
17212 BC NA NA -123.0724 38.93073
17213 C NA NA -123.7240 41.84403
17214 <NA> 464 NA -122.9430 38.30988
17215 C NA NA -123.4442 40.65369
17216 BC NA NA -122.9389 38.31551
17217 C NA NA -123.0747 38.97998
17218 C NA NA -123.6580 41.59610
17219 C NA NA -123.4513 40.70992
17220 C NA NA -123.0901 39.06473
17221 BC NA NA -123.0653 38.94845
17222 BC NA NA -122.9464 38.36808
17223 <NA> 464 NA -123.0143 38.70205
17224 <NA> NA 5 -122.8609 37.94137
17225 <NA> NA 5 -122.8628 37.95057
17226 <NA> NA 7 -122.8646 37.95978
If I wanted to find the row with Lat = 37.95978, how would i do that? How
would I find the rows with BC?
Thank you for all your help!
Mehdi Khan
On Tue, Jul 21, 2009 at 12:10 PM, Steve Lianoglou <
mailinglist.honey...@gmail.com> wrote:
> I am a bit confused as to what the following command does:
>> evens <- df$nums %% 2 == 0
>>
>
> It returns a logical vector (I'm calling this an "indexing vector") that is
> TRUE where df$nums %% 2 == 0 (%% is modulo division, and 4 mod 2 == 0 -- so
> it's a test for "being even")
>
> In my matrix example, let's say I am looking for the variable(s) BC and I
>> want R to return all the rows with that value...
>>
>
> You "just" have to setup a suitable test and build an "indexing" vector to
> select the appropriate rows -- or use the subset function (see ?subset).
>
> If it's still confusing to you, please create a trivial example data.frame
> and send it back to the list along with things you'd like to "find", so we
> can give you concrete examples on different ways you can find what you need.
>
> or If I want a value such as 33.543. How would I get it to do that?
>> Just a single value in the latter case. I have already converted it to a
>> data frame.
>>
>
> Be careful when searching for doubles/floats as sometimes you'll miss what
> you're looking for if you are using exact matches (ie something ==
> something.else) ... I have an almost.equals function in my "bag of
> utilities" that I'd probably use for stuff like this:
>
> almost.equal <- function(x, y, eps=0.000001) {
> abs(x - y) < eps
> }
>
> '%~%' <- function(x, y) almost.equal(x, y))
>
> R> x <- rnorm(1000, sd=.0001)
> R> sum(x %~% 0)
> ## Equivalently: sum(almost.equal(x, 0))
> [1] 8
>
> R> sum(x == 0)
> [1] 0
>
> Summing over a logical vector treats the TRUE values as 1 and FALSE values
> as 0.
>
> HTH,
>
> -steve
>
> --
> Steve Lianoglou
> Graduate Student: Physiology, Biophysics and Systems Biology
> Weill Medical College of Cornell University
>
> Contact Info:
> http://cbio.mskcc.org/~lianos/contact<http://cbio.mskcc.org/%7Elianos/contact>
>
>
>
>
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