[R] Extracting the first element of a list

Uwe Ligges ligges at amadeus.statistik.uni-dortmund.de
Wed Mar 27 13:12:28 CET 2002

```Ko-Kang Kevin Wang wrote:
>
> Hi,
>
> ----- Original Message -----
> From: "Uwe Ligges" <ligges at amadeus.statistik.uni-dortmund.de>
> To: "Ross Darnell" <r.darnell at shrs.uq.edu.au>
> Cc: <r-help at stat.math.ethz.ch>
> Sent: Wednesday, March 27, 2002 8:03 PM
> Subject: Re: [R] Extracting the first element of a list
>
> > For the first element of a list L:
> >  L[[1]]
> > For the first elements of all elements (vector) of the list:
> >  lapply(L, function(x) x[1])
>
> So, suppose I've got a vector called foo, which has elements as follows:
>   305 159 251 215 101 224 306 199 194 325 329 221 318 238  17 ....
> (the rest omittied)
>
> And suppose I want to extract out the first digit of each number, so like:
>   3 1 2 2 1 2 3 1 1 3 3 2 3 2 1...
>
> Do I still use
>   lapply(foo, function(x) x[1])
> it doesn't seem to work...

Well, I meant *after* strsplit:

temp <- strsplit(foo, "")
L <- lapply(temp, function(x) x[1])
as.numeric(unlist(L))

In this case you can also calculate it:

floor(foo / (10^floor(log(foo, 10))))

Uwe Ligges
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