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Inconsistent replacement of list column element with NULL in table with 1 row #5558

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tdhock opened this issue Dec 8, 2022 · 1 comment · May be fixed by #6167
Open

Inconsistent replacement of list column element with NULL in table with 1 row #5558

tdhock opened this issue Dec 8, 2022 · 1 comment · May be fixed by #6167
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consistency

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@tdhock
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tdhock commented Dec 8, 2022

In base R data.frame we can replace an element of a list column with NULL via:

> DF1=data.frame(L=I(list("A")),i=1)
> DF1$L=list(NULL)
> DF1
     L i
1 NULL 1

However in data.table, doing that results in deleting the list column entirely:

> DT1=data.table(L=list("A"),i=1)
> DT1$L=list(NULL)
> DT1
       i
   <num>
1:     1

Request: can we make the above code do a replacement (like base R data.frame) instead of deleting the column?

The above issue is confusing because it is inconsistent with how data table handles replacement in tables with more than one row:

> DT2=data.table(L=list("B","C"),i=1)
> DT2$L <- list(NULL,NULL)
> DT2
        L     i
   <list> <num>
1:            1
2:            1
> DF2=data.frame(L=I(list("B","C")),i=1)
> DF2$L <- list(NULL,NULL)
> DF2
     L i
1 NULL 1
2 NULL 1

Actually, we can do the replacement (inconsistently) in data.table via

> DT1=data.table(L=list("A"),i=1)
> DT1$L=list(list(NULL))
> DT1
        L     i
   <list> <num>
1:            1
@avimallu
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avimallu commented Dec 8, 2022

I can do this:

library(data.table)
DT1=data.table(L=list("A"),i=1)
DT1[, `:=`(L = list(NULL))]

that works, but oddly not

DT1[, L := list(NULL)]

which should be identical per data.table documentation.

@tdhock tdhock changed the title can not replace list column element with NULL in table with 1 row Inconsistent replacement of list column element with NULL in table with 1 row Dec 9, 2022
@joshhwuu joshhwuu mentioned this issue May 27, 2024
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@joshhwuu joshhwuu linked a pull request Jun 4, 2024 that will close this issue
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Consistent Replacement of List Column with NULL Rdatatable/data.table
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@tdhock @avimallu