[R] how to pass multiple pattern varibles to grep()

[Bert Gunter]

"The | symbol has a completely different meaning in R syntax than it
has in regular expression syntax."

Well, actually it doesn't -- loosely speaking, they both mean "or" (ok
-- interpreting concatenation as "or" is a bit of a stretch). Perhaps
to clarify your statement (stop here if none is needed!):

1) z|v  is an R expression that evaluates to the disjunction of the
values of objects z and v, which should be logical (and will be
coerced to logicals if needed and possible). That is, the result is
logical,

2) paste(z,v, sep = "|") evaluates to a character string which is the
concatenation of character string values of z and v with "|" in the
middle. regex needs character strings to define its patterns.

Clear?

Cheers,
Bert





Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Fri, Sep 23, 2016 at 9:34 AM, Jeff Newmiller
<jdnewmil at dcn.davis.ca.us> wrote:
> The | symbol has a completely different meaning in R syntax than it has in
> regular expression syntax. R hands of pattern strings to the regex library
> without looking inside the strings any more than it has to. Likewise, the
> regex library has no clue about R syntax. Your attempt failed to create a
> character string for grep to give to the regex library. To do that read
> ?paste.
>
> grep( paste( z, v, sep = "|" ), a )
>
>
> On Thu, 22 Sep 2016, Fix Ace via R-help wrote:
>
>> Hello, there,
>> My patterns are defined by variables, for example:z="h"v="x"
>> I have a vector: a=c("th","mx","t")
>> I would like to find elements in vector a that contain either "h", or "x"
>> grep("h|x", a) apparently works. However, when I tried: grep(z|v,a), it
>> did not work. Can anyone help how to handle such situation?
>> Thanks.
>> Ace
>>    On Wednesday, March 18, 2015 5:52 PM, Fix Ace <acefix at rocketmail.com>
>> wrote:
>>
>>
>> Thank you very much!
>> I do need to learn more about R!!
>>
>>     On Tuesday, March 17, 2015 9:26 PM, William Dunlap <wdunlap at tibco.com>
>> wrote:
>>
>>
>> Fix Ace wrote    What is the default "n"?
>> 512:   > length(density(rnorm(10^6))$x)   [1] 512   >
>> args(density.default)   function (x, bw = "nrd0", adjust = 1, kernel =
>> c("gaussian",        "epanechnikov", "rectangular", "triangular",
>> "biweight",        "cosine", "optcosine"), weights = NULL, window = kernel,
>> width, give.Rkern = FALSE, n = 512, from, to, cut = 3, na.rm = FALSE,
>> ...)   NULL   > ?density # or ?density.default, should also tell you about
>> its meaning
>>
>> Bill Dunlap
>> TIBCO Software
>> wdunlap tibco.com
>> On Tue, Mar 17, 2015 at 7:02 PM, Fix Ace <acefix at rocketmail.com> wrote:
>>
>> Thank you for the email.
>> What is the default "n"?
>> Thanks!
>>
>>     On Tuesday, March 17, 2015 4:06 PM, William Dunlap <wdunlap at tibco.com>
>> wrote:
>>
>>
>> Increasing the value of 'n' given to density will give an estimate at more
>> points so it will look smoother.  Try n=2^18.
>> Bill Dunlap
>> TIBCO Software
>> wdunlap tibco.com
>> On Tue, Mar 17, 2015 at 12:06 PM, Fix Ace <acefix at rocketmail.com> wrote:
>>
>>
>>
>>  I have a dataset with 6187 elements, ranged from 3 to 104028. When I
>> tried to examine only small range of data, I found that the plot was not
>> smooth (as shown below):
>> plot(density(test$V2), xlim=c(0,1000))
>>
>>
>>  Is there away to make it smoother?
>> Thanks a lot!!
>>
>>
>>
>>
>>
>>
>>
>>
>>   ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>         [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
> ---------------------------------------------------------------------------
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>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.