[R] subset problem

[peter dalgaard]

On Mar 29, 2012, at 07:25 , reeyarn wrote:

> Hi,
> 
> If my data frame "df" has a index "type", I want to get a subset such
> that the type belongs to a "type_list";
> using sql, I want
>  SELECT name, type FROM df
>    WHERE type in type_list;
> 
> Now in R I have to write a loop like
>  mysubset<- df [ df$type == type_list[1], ]
>  for (type1 in type_list[ 2: length (type_list) ] ) {
>    mysubset<-cbind (mysubset, df [ df$type == type1, ])
>  }
> 
(that should be rbind(), I believe)

> What is the natural way of doing this in R? Is it possible to use
> subset() to attain this?

%in% is your friend

mysub <- subset(df, type %in% type_list, select=c(name,type))

or 

mysub <- df[df$type %in% type_list, c("name","type")]

The latter is slightly safer if you can't be sure that df doesn't contain a column called type_list. 

> Thanks!
> 
> Best,
> Reeyarn
> 
> On Fri, Dec 3, 2010 at 11:26 AM,  William Dunlap <[hidden email]> wrote:
>> HI,
>> I have a dataframe like this:
>> name    type
>> A          t1
>> B           t2
>> C          t1
>> D           t4
>> E           t3
>> F            t2
>> how can I have a "sub dataframe" based with the column "type" like this:
>> (for type = t1)
>> name    type
>> A          t1
>> C          t1
>> D           t1
> 
> Hi,
> 
> Let's say your data.frame is stored in a variable named "df":
> 
> R> subset(df, type == 't1')
> 
> Read the help files:
> 
> R> ?subset
> 
> Also take a look at ?split
> 
> -steve
> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com