Write `move {}.before {}`

[Jolanrensen]

We have move after but move before was never finished.

[CarloMariaProietti]

Hey, I would like to work on this issue.

[Jolanrensen]

@CarloMariaProietti go ahead and give it a try :) When I looked at it, it was a bit more complex than expected, so let me know if you need any help.

Feel free to ignore compiler plugin support for now (the @Refine @Interpretable stuff). If move {}.before {} works, we can add it later.

There's no need to create overloads for functions we annotated with @Deprecated(DEPRECATED_ACCESS_API) @AccessApiOverload as they are going to be removed in a future version of DataFrame.

[CarloMariaProietti]

I have been trying for a few days but for now I did not succed. It would be great if you could help!

[Jolanrensen]

How far did you get? :) Did you find the MoveClause.afterOrBefore()` implementation function?

The way I think that function works is:

• it first removes all columns selected by the move {} operatation,
• it does some checking to see whether the move is not done to a "deeper level" (aka we cannot move a column group into itself),
• then it finds the position of the reference inside after {} or before {} as refNode,
• and finally, all columns that were removed get turned into a ColumnToInsert with the given refNode/referenceNode and passed on to the insert implementation.

Apparently, insertImpl is the one that decides that these columns should be placed after the one referenced.

That seems to be done here:

dataframe/core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/insert.kt

Line 83 in 82bf7ba

if (it.referenceNode == null) {

There appears to be some logic in there that gives a new index for the columns to be inserted relative to the provided referenceNode from ColumnToInsert.

Maybe you could try adding an extra parameter to ColumnToInsert, like insertAfterReferenceNode: Boolean = true and adapt the behavior in insertImpl depening on this flag.

It's probably the easiest to create some of the API first, so you can write some tests with expected behavior (for instance, dataFrameOf("a", "b", "c")(0, 0, 0).move { "b" and "c" }.before("a").columnNames() shouldBe listOf("b", "c", "a")). And try to see if it works with column groups as well, like after {}.

Good luck :) let me know how it goes!

[CarloMariaProietti]

Thank you very much! I have been looking to moveAfterOrBefore and I also think that the logic of "after" is inside InsertImpl. I will try to follow your advice and implement it.

[CarloMariaProietti]

I made it! I tried my best to implement the strategy you suggested me but I did not succeed. In the end I solved the issue only working on MoveClause.afterOrBefore().