user2999110 - 6 months ago 33

R Question

I have a data frame as

`A: V1 V2`

1 3

1 4

3 4

1 6

6 5

I want output which satisfies transitive property on V1 and V2

`B: V1 V2 V3`

1 3 4

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Answer Source

The idea is you select one source and try to find the transitivity with two targets. if those are the same then you have the right combination.

I add additional columns for debug purpose, but the query can be simplify a little bit more.

```
SELECT *
FROM (
SELECT source.[V1], source.[V2],
target1.[V1] as t1_v1,
target1.[V2] as t1_v2,
target2.[V1] as t2_v1,
target2.[V2] as t2_v2,
CASE WHEN source.[V1] = target1.[V1]
THEN target1.[V2]
ELSE target1.[V1]
END as transitive1,
CASE WHEN source.[V2] = target2.[V2]
THEN target2.[V1]
ELSE target2.[V2]
END as transitive2
FROM A as source
JOIN A as target1
ON (source.[V1] = target1.[V1] OR source.[V1] = target1.[V2])
AND NOT (source.[V1] = target1.[V1] AND source.[V2] = target1.[V2])
JOIN A as target2
ON (source.[V2] = target2.[V1] OR source.[V2] = target2.[V2])
AND NOT (source.[V1] = target2.[V1] AND source.[V2] = target2.[V2])
) T
WHERE T.transitive1 = T.transitive2
```

**OUTPUT**

To get the result you want select the right columns and add aditional filter

```
SELECT T.[V1] as [V1],
T.[V2] as [V2],
T.[transitive1] as [V3]
....
WHERE T.[V1] > T.[V2]
AND T.[V2] > T.[transitive1]
AND T.transitive1 = T.transitive2
```

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