CODEWITHSUNDEEP
rdataframedata.table
Amin
Amin

Reputation: 57

Grouping in Embedded Group Structures in R data.table

I have a data.table object looks like this:

FamilyID InterFamilyID MumInFamilyID Edu
1        1             NA            2
1        2             NA            5
1        3             2             3
2        1             NA            6
2        2             1             9
2        2             1             3

I want to perform a query like this one:

tbl1[, MumEdu:= Edu[InterFamilyID == MumInFamilyID], by=FamilyID]

to get something like this: 

FamilyID InterFamilyID MumInFamilyID Edu MumEdu
1        1             NA            2   NA
1        2             NA            5   NA
1        3             2             3   5
2        1             NA            6   NA
2        2             1             9   6
2        2             1             3   6

In fact I have a data.table grouped by a column (FamilyID) and each of these groups are 1-1 grouped by another column (InterFamilyID). In another column there is reference to smaller group id of another group member. I want to use these values to access the referenced rows values.

Upvotes: 1

Views: 38

Answers (1)

akuiper
akuiper

Reputation: 215057

You can use match to:

returns a vector of the positions of (first) matches of its first argument in its second.

and use the result positions to find out the corresponding element in Edu column:

tbl1[, MumEdu := Edu[match(MumInFamilyID, InterFamilyID)], by = FamilyID]
tbl1
#   FamilyID InterFamilyID MumInFamilyID Edu MumEdu
#1:        1             1            NA   2     NA
#2:        1             2            NA   5     NA
#3:        1             3             2   3      5
#4:        2             1            NA   6     NA
#5:        2             2             1   9      6
#6:        2             2             1   3      6

Upvotes: 1

Related Questions