Joining datasets on a non-distinct attribute
Hi rapidminers,
Let's say I need to JOIN 2 datasets, A and B, on an attribute 'key'.
It is distinct for dataset A (each distinct value corresponds to only one example), but not for B (there are few examples with the same value of 'key' in 
.
What logic of joining will RapidMiner follow in this case? For each join 'A <--> key <--> B' what exactly example will be taken from B? First, last, random, or it totally depends on how dataset was stored in repo so it's not possible to know at all?
Thank you.
Best Answer
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So the short version is that it will REPEAT all of the id examples with the different B values:
Data Set 1 Data Set 2
ID Last ID First
1 JONES 2 Lynn
2 HOLMES 2 Lucile
3 SILVA 2 Leonardo
After inner join:
ID Last First
2 HOLMES Lynn
2 HOLMES Lucile
2 HOLMES Leonardo
After outer join:
ID Last First
2 HOLMES Lynn
2 HOLMES Lucile
2 HOLMES Leonardo
1 JONES ?
3 SILVA ?
left join is same as inner join in this case
After right join:
ID Last First
1 JONES ?
2 HOLMES Lynn
2 HOLMES Lucile
2 HOLMES Leonardo
3 SILVA ?
Clear as mud?
Scott
2
Altair EmployeeAnswers
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So first it depends on which join you’re doing: inner, outer, left or right. You will most likely get different results depending on the data. Which one are you doing?0
-
So the short version is that it will REPEAT all of the id examples with the different B values:
Data Set 1 Data Set 2
ID Last ID First
1 JONES 2 Lynn
2 HOLMES 2 Lucile
3 SILVA 2 Leonardo
After inner join:
ID Last First
2 HOLMES Lynn
2 HOLMES Lucile
2 HOLMES Leonardo
After outer join:
ID Last First
2 HOLMES Lynn
2 HOLMES Lucile
2 HOLMES Leonardo
1 JONES ?
3 SILVA ?
left join is same as inner join in this case
After right join:
ID Last First
1 JONES ?
2 HOLMES Lynn
2 HOLMES Lucile
2 HOLMES Leonardo
3 SILVA ?
Clear as mud?
Scott
2 -
Clear, Captain.
Thanks
1 -
Captain Morgan!
2
