[R] grep() exclude certain patterns?

Peng Yu pengyu.ut at gmail.com
Sat Dec 5 02:55:37 CET 2009 

On Fri, Dec 4, 2009 at 7:51 PM, Charles C. Berry <cberry at tajo.ucsd.edu> wrote:
> On Fri, 4 Dec 2009, Peng Yu wrote:
>
>> On Fri, Dec 4, 2009 at 2:35 PM, Greg Snow <Greg.Snow at imail.org> wrote:
>>>
>>> The invert argument seems a likely candidate, you could also do perl=TRUE
>>> and use negations within the pattern (but that is probably overkill for your
>>> original question).
>>
>> I don't see 'invert' in the R version (2.7.1) that I use. Here is the
>> snip from ?grep
>
> PLEASE! There have been SEVEN (7) releases of R since 2.7.1.
>
> Upgrade to R.10.0 NOW!

This is not under my control. The R installed on the system that I use
won't be updated by the system administrator, now. But it might be at
a later time.

> This is the second time in a few days that you have not been able to
> follow/understand advice given to you on this list because you are using an
> older version of R, while the rest of us have moved on.
>
> Chuck
>
>
>>
>> Usage:
>>
>>    grep(pattern, x, ignore.case = FALSE, extended = TRUE,
>>         perl = FALSE, value = FALSE, fixed = FALSE, useBytes = FALSE)
>>
>>    sub(pattern, replacement, x,
>>        ignore.case = FALSE, extended = TRUE, perl = FALSE,
>>        fixed = FALSE, useBytes = FALSE)
>>
>>    gsub(pattern, replacement, x,
>>         ignore.case = FALSE, extended = TRUE, perl = FALSE,
>>         fixed = FALSE, useBytes = FALSE)
>>
>>    regexpr(pattern, text, ignore.case = FALSE, extended = TRUE,
>>            perl = FALSE, fixed = FALSE, useBytes = FALSE)
>>
>>    gregexpr(pattern, text, ignore.case = FALSE, extended = TRUE,
>>             perl = FALSE, fixed = FALSE, useBytes = FALSE)
>>
>>
>>> Could you explain to us the process that you use to search for answers to
>>> your questions before posting?  You have been asking quite a few questions
>>> that have answers out there if you can find them.  If you tell us where you
>>> are looking (and why) then we may be able to suggest some different search
>>> strategies that will help you find the answers quicker.  Also knowing your
>>> thought process may help us in designing future help/tutorials that cater
>>> more to people learning R for the first time, things that seem obvious to
>>> those of us who have been using the current documentation, apparently are
>>> not that obvious to some new users (but also realize that the first place
>>> that you may think to look may not even occur to some of us that learned
>>> computers in a different time, see fortune(89) ).
>>
>> For this particular problem in the original post, it is due to the
>> fact that I use an older R.
>>
>> But in general, the R help and examples in the help page should be
>> improved in terms of the structure. Just as we write a paper, it is
>> better to have a hierarchical descriptions (i.e., which is similar to
>> the flow of abstract -> introduction -> maintext, in each section that
>> appears later, more detailed information should be given; but earlier
>> section should give readers general ideas.)
>>
>> The current way to organizing the help is less satisfactory.
>> Description->Usage->Arguments
>>
>> This may be good if you have already what you should look for. But if
>> you are new to it, you will be easily lost. For example, many
>> functions are given in Usage without been explained what the
>> difference between them until very late, or no explicit explanations
>> at all. But having such descriptions on the differences can help users
>> choose the appropriate ones.
>>
>> Some of informative examples should be put forward to help newbies
>> understand how to use each function, rather than put at the end of the
>> help page. Many examples in the help page requires previous knowledge
>> in other functions. In general, it is better to have the information
>> on each help page self contained.
>>
>> Another problem is not due to the help of R, but the design of R
>> itself --- there many specially case to use a function. For example,
>> x[1:2,] is a matrix but x[1,] is a vector.
>>
>>> x=matrix(1:6,nr=3)
>>> x[1:2,]
>>
>>    [,1] [,2]
>> [1,]    1    4
>> [2,]    2    5
>>>
>>> x[1,]
>>
>> [1] 1 4
>>
>> I know that somebody that has worked with R for over 10 years don't
>> know why (It may be because he doesn't care). But I have to ask the
>> mailing list to understand that I have to use the option 'drop' in
>> order to get a matrix as the returned value.
>>>
>>> x[1,,drop=F]
>>
>>    [,1] [,2]
>> [1,]    1    4
>>
>> If I were the original designer of R, I would make the interface more
>> orthogonal (this is the usual way to reduce complexity in software).
>> For example, [] would always return a matrix, if I want to reduce its
>> dimension, I will have another function to do so.
>>
>> Have many special cases although might be convenient in some cases.
>> But they may also cause confusions and may cause some delicate bugs
>> that are to figure out especially to newbies.
>>
>> The above are my current thoughts. Let me know if it makes sense to you or
>> not.
>>
>>>> -----Original Message-----
>>>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>>>> project.org] On Behalf Of Peng Yu
>>>> Sent: Friday, December 04, 2009 12:43 PM
>>>> To: r-help at stat.math.ethz.ch
>>>> Subject: Re: [R] grep() exclude certain patterns?
>>>>
>>>> On Fri, Dec 4, 2009 at 11:54 AM, Duncan Murdoch <murdoch at stats.uwo.ca>
>>>> wrote:
>>>>>
>>>>> On 04/12/2009 12:52 PM, Peng Yu wrote:
>>>>>>
>>>>>> The external grep program has an option -v to select non-matching
>>>>>> lines. I'm wondering if how to exclude certain patterns in grep() in
>>>>>> R?
>>>>>>
>>>>>
>>>>> ?grep
>>>>
>>>> I don't see which argument to use.
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list
>>>> 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.
>>>
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> 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.
>>
>
> 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
>
>

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