R help - Feb 2012 - Wildcard for indexing?

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
--

On 14/02/2012 9:54 AM, Johannes Radinger 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
Try grepl():

a[grepl("^[AB]", a)]

is probably the simplest way for your example.

Duncan Murdoch

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_")

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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http://www.R-project.org/posting-guide.html
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Hi,

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
Do you want elements that start with A or B, as you state above, or elements
that start with A_A or A_B as here?

Either way, this is a job for grepl(), and it is quite easy:
> a <-
c("A_A","A_B","C_A","BB","A_Asd")
>
> grepl("^[AB]", a)
[1]  TRUE  TRUE FALSE  TRUE  TRUE
> grepl("^A_[AB]", a)
[1]  TRUE  TRUE FALSE FALSE  TRUE

Sarah


-- 
Sarah Goslee
http://www.functionaldiversity.org