[datatable-help] (no subject)

[jim holtman]

Is this what you want:

> require(data.table)
> DT <- data.table('id1'=c(1,1,1,1,2,2,2,2,3,3,3,3)
+      , 'id2'= c(1,2,3,4)
+      , 'val'=c(1,2,NA,5,1,NA,NA,4,NA,2,4,6)
+      , key=c("id1", "id2"))
> require(zoo)
> result <- DT[
+     , list(val = na.locf(val, na.rm = FALSE))
+     , by = id1
+     ]
> result
      id1 val
 [1,]   1   1
 [2,]   1   2
 [3,]   1   2
 [4,]   1   5
 [5,]   2   1
 [6,]   2   1
 [7,]   2   1
 [8,]   2   4
 [9,]   3  NA
[10,]   3   2
[11,]   3   4
[12,]   3   6

On Tue, Feb 7, 2012 at 8:34 AM, DUPREZ Cédric <Cedric.DUPREZ at ign.fr> wrote:
> Dear all,
>
> I am looking for the best way to complete missing values in a datatable, according to particular rules.
>
> Having the following datatable:
> DT <- data.table('id1'=c(1,1,1,1,2,2,2,2,3,3,3,3)
>      , 'id2'= c(1,2,3,4)
>      , 'val'=c(1,2,NA,5,1,NA,NA,4,NA,2,4,6)
>      , key=c("id1", "id2"))
>
> I get:
>      id1 id2 val
>  [1,]   1   1   1
>  [2,]   1   2   2
>  [3,]   1   3  NA
>  [4,]   1   4   5
>  [5,]   2   1   1
>  [6,]   2   2  NA
>  [7,]   2   3  NA
>  [8,]   2   4   4
>  [9,]   3   1  NA
> [10,]   3   2   2
> [11,]   3   3   4
> [12,]   3   4   6
>
> The rule to complete missing values is the following: put the immediatly preceding value (val) from the same id1 line that is not missing.
> In my example, lines with missing values are :
>
> DT[is.na(val)]
>
>     id1 id2 val
> [1,]   1   3  NA
> [2,]   2   2  NA
> [3,]   2   3  NA
> [4,]   3   1  NA
>
> The final result for my datatable should be:
>
> DT
>      id1 id2 val
>  [1,]   1   1   1
>  [2,]   1   2   2
>  [3,]   1   3   2
>  [4,]   1   4   5
>  [5,]   2   1   1
>  [6,]   2   2   1
>  [7,]   2   3   1
>  [8,]   2   4   4
>  [9,]   3   1  NA
> [10,]   3   2   2
> [11,]   3   3   4
> [12,]   3   4   6
>
> What is the best and easiest way to complete missing values with such rules. I tried with joins and := operator by often get error messages like "combining bywithoutby with := in j is not yet implemented."
>
> Thanks in advance for your help,
>
> Cedric
>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.