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indices/key2 should return list #1589

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jangorecki opened this issue Mar 12, 2016 · 1 comment
Closed

indices/key2 should return list #1589

jangorecki opened this issue Mar 12, 2016 · 1 comment
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@jangorecki
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@jangorecki jangorecki commented Mar 12, 2016

There can be multiple indices on single data.table, each index can be set on multiple fields.
The most correct representation then is to return list of vectors.
Current behavior:

library(data.table)
dt = data.table(a=1,b=2,c=3,d=4)
setindexv(dt, "a")
setindexv(dt, c("a","b"))
setindexv(dt, c("b","a"))
setindexv(dt, c("d","c","a"))
indices(dt)
#[1] "a"       "a__b"    "b__a"    "d__c__a"

Expected

list("a", c("a","b"), c("b","a"), c("d","c","a"))
#[[1]]
#[1] "a"
#
#[[2]]
#[1] "a" "b"
#
#[[3]]
#[1] "b" "a"
#
#[[4]]
#[1] "d" "c" "a"

There could be an additional argument forcing to return a vector instead of list by collapsing column names.

sapply(list("a", c("a","b"), c("b","a"), c("d","c","a")), paste, collapse=",")
#[1] "a"     "a,b"   "b,a"   "d,c,a"
@mattdowle
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@mattdowle mattdowle commented Dec 5, 2016

Minor reopen to address: 3aa65e2#commitcomment-20075531

@mattdowle mattdowle reopened this Dec 5, 2016
@mattdowle mattdowle removed this from the Candidate milestone Jan 31, 2017
@mattdowle mattdowle added this to the v1.10.2 milestone Jan 31, 2017
@mattdowle mattdowle added this to the v1.10.2 milestone Jan 31, 2017
@mattdowle mattdowle removed this from the Candidate milestone Jan 31, 2017
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