[R] Get the location of a numeric element in a list

[Mohammad Tanvir Ahamed]

Thanks Martin Morgan. Thats works excellent on a large data . 
 Tanvir Ahamed 
Göteborg, Sweden   |  mashranga at yahoo.com 


----- Original Message -----
From: Martin Morgan <martin.morgan at roswellpark.org>
To: Mohammad Tanvir Ahamed <mashranga at yahoo.com>; R-help Mailing List <r-help at r-project.org>
Sent: Tuesday, 28 June 2016, 11:07
Subject: Re: [R] Get the location of a numeric element in a list

On 06/28/2016 03:03 AM, Mohammad Tanvir Ahamed via R-help wrote:
> Can any one please help me. I will apply this for a very large list, about 400k vector in a list and vector size is unequal and large
>
> Example :
> Input:
> a <- c(1,3,6,9,25,100)
> b<-c(10,7,20,2,25)
> c<-c(1,7,5,15,25,300,1000)
> d<-list(a,b,c)
>
> Expected outcome :
> # When looking for 1 in d
> c(1,3)
>
> # When looking for 7 in d
>
> c(2,3)
>
> # when looking for 25 in d
> c(1,2,3)
> # When looking for 50 in d
> NULL or 0

Make a vector of queries

     queries = c(1, 7, 25, 50)

Create a factor of unlist(d), using queries as levels. Create a vector 
rep(seq_along(d), lengths(d)), and split it into groups defined by f

     f = factor(unlist(d, use.names=FALSE), levels=queries)
     split(rep(seq_along(d), lengths(d)), f)

Martin Morgan


>
>
> Thanks in advance !!
>
>
>
>
>
> Tanvir Ahamed
> Göteborg, Sweden  |  mashranga at yahoo.com
>
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> and provide commented, minimal, self-contained, reproducible code.
>


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