Joining datasets on a non-distinct attribute

kypexin

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. 

sgenzer

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