[R] How to get the rowindices without using which?

[Peter Dalgaard]

Martin Lam <tmlammail at yahoo.com> writes:

> Hi,
> 
> I was wondering if it is possible to get the
> rowindices without using the function "which" because
> I don't have a restriction criteria. Here's an example
> of what I mean:
> # take 10 randomly selected instances
> iris[sample(1:nrow(iris), 10),]
> 
> # output
>     Sepal.Length Sepal.Width Petal.Length Petal.Width 
>   Species
> 76           6.6         3.0          4.4         1.4
> versicolor
> 105          6.5         3.0          5.8         2.2 
> virginica
> 131          7.4         2.8          6.1         1.9 
> virginica
> 79           6.0         2.9          4.5         1.5
> versicolor
> 69           6.2         2.2          4.5         1.5
> versicolor
> 42           4.5         2.3          1.3         0.3 
>    setosa
> 25           4.8         3.4          1.9         0.2 
>    setosa
> 129          6.4         2.8          5.6         2.1 
> virginica
> 60           5.2         2.7          3.9         1.4
> versicolor
> 80           5.7         2.6          3.5         1.0
> versicolor
> 
> What I want to get are their rownumbers: 76, 105, 131,
> 79, 69, 42, 25, 129, 60, 80.

Er, they are either the rownames of the result or the value that you
used to index with:

iris[nums <- sample(1:nrow(iris), 10),]

leaves the numbers sitting in nums. 

(If the original data frame has rownames that are not 1:nrow(yourframe),
then you have to decide whether it is names or numbers that you want.)

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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