R help - Apr 2013 - Removing multiple elements from a vector or list

Hi,
?vec1<- letters
vec1[!grepl("b|r|x",alp)]
# [1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
#[20] "v" "w" "y" "z"
?vec1[!vec1%in% c("b","r","x") ]
# [1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
#[20] "v" "w" "y" "z"

alp<-lapply(seq_along(vec1),function(i) vec1[i])
?res<-alp[!grepl("b|r|x",alp)]
unlist(res)
# [1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
#[20] "v" "w" "y" "z"
unlist(alp[!alp%in%c("b","r","x")])
?#[1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
#[20] "v" "w" "y" "z"
A.K.
>If I for example have a list (or vector) ?that contains all the letters in
the alphabet.
>
>alp <-
list("a","b","c",......................."z")
?this is of course not the exact code
>
>How can I remove multiple elements at one time without knowing their
location in the list. Say I want to remove b,r,x?
>Same question if apl is a vector 
>
>I have tried 
>
>alp <- alp[-c("b","r","x")] 
>
>this does not work 
>
>Thanks, 
>Johnny

On Apr 15, 2013, at 2:30 PM, arun wrote:
> Hi,
>  vec1<- letters
alp <- as.list(letters) would have constructed the vector that was described.
> vec1[!grepl("b|r|x",alp)]
> # [1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
> #[20] "v" "w" "y" "z"
>  vec1[!vec1%in% c("b","r","x") ]
> # [1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
> #[20] "v" "w" "y" "z"
> 
> alp<-lapply(seq_along(vec1),function(i) vec1[i])
>  res<-alp[!grepl("b|r|x",alp)]
> unlist(res)
> # [1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
> #[20] "v" "w" "y" "z"
> unlist(alp[!alp%in%c("b","r","x")])
>  #[1] "a" "c" "d" "e" "f"
"g" "h" "i" "j" "k"
"l" "m" "n" "o" "p"
"q" "s" "t" "u"
> #[20] "v" "w" "y" "z"
> A.K.
All good. There would be an additional way to do this if the list were first
assigned names. (At the moment the list only has positions for reference.)

alp <- setNames(alp, letters[1:26])
# Something like that initial code would succeed:

alp <- alp[ !names(alp) %in% c("b","r","x")]

The result is still a list.

> 
>> If I for example have a list (or vector)  that contains all the letters
in the alphabet.
>> 
>> alp <-
list("a","b","c",......................."z")
this is of course not the exact code
>> 
>> How can I remove multiple elements at one time without knowing their
location in the list. Say I want to remove b,r,x?
>> Same question if apl is a vector 
>> 
>> I have tried 
>> 
>> alp <- alp[-c("b","r","x")] 
You _cannot_use_negative_indexing_with_names (or values). You could have used
logical indexing:

alp [ sapply(alp, function(x) !x %in%
c("b","r","x") ) ]

# OR perhaps the most compact solution offered so far;  numeric indexing with
the minus unary operator:

alp[ -grep("b|r|x", alp) ]

-- 

David Winsemius
Alameda, CA, USA