[R] Wildcard for indexing?
Duncan Murdoch
murdoch.duncan at gmail.com
Tue Feb 14 16:19:43 CET 2012
On 14/02/2012 10:10 AM, Johannes Radinger wrote:
> Hi,
>
> -------- Original-Nachricht --------
> > Datum: Tue, 14 Feb 2012 09:59:39 -0500
> > Von: "R. Michael Weylandt"<michael.weylandt at gmail.com>
> > An: Johannes Radinger<JRadinger at gmx.at>
> > CC: R-help at r-project.org
> > Betreff: Re: [R] Wildcard for indexing?
>
> > I think the grep()-family (regular expressions) will be the easiest
> > way to do this, though it sounds like you might prefer grepl() which
> > returns a logical vector:
> >
> > ^[AB] # Starts with either an A or a B
> > ^A_ # Starting with A_
> >
> > a<- c("A_A","A_B","C_A","BB","A_Asd"
> > grepl("^[AB]", a)
> > grepl("^A_")
>
> Yes grepl() is what I am looking for.
> is there also something like an OR statement e.g. if I want to
> select for elements that start with "as" OR "df"?
grepl("^(as|df)", a)
should work. See ?regexp for all the possibilities, rules about
operator precedence, etc. (Or just use grepl("^as", a) | grepl("^df", a).)
Duncan Murdoch
> /johannes
>
> >
> > Michael
> >
> > On Tue, Feb 14, 2012 at 9:54 AM, Johannes Radinger<JRadinger at gmx.at>
> > wrote:
> > > Hi,
> > >
> > > I'd like to know if it is possible to use wildcards * for indexing...
> > > E.g. I have a vector of strings. Now I'd like to select all elements
> > > which start with A_*? I'd also need to combine that with logical
> > operators:
> > >
> > > "Select all elements of a vector that start with A (A*) OR that start
> > with B (B*)"
> > >
> > > Probably that is quite easy. I looked into grep() which I think might
> > perform such tasks, but probably there is a more straigth forward solution.
> > >
> > > a<- c("A_A","A_B","C_A","BB","A_Asd")
> > > a[a=="A_A"| a=="A_B"] # here I'd like an index but with wildcard
> > >
> > > /johannes
> > > --
> > >
> > > ______________________________________________
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> > > 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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