Feature Request : Reshape Data within DataTable

[samukweku]

• convert data from wide to long, and vice versa (similar to melt/dcast in rdatatable or melt/pivot.pd.wide_to_long in pandas)

Example :

df = dt.Frame({"A":['a','b','c'], "B":[1,3,5],"C":[2,4,6]})

Transform from wide to long :

# new shape:

A variable value
0 a B 1
1 b B 3
2 c B 5
3 a C 2
4 b C 4
5 c C 6

Transform from long to wide :
A B C
0 a 1 2
1 b 3 4
2 c 5 6

It would also be beneficial if there was flexibility in the reshaping, something similar to patterns in rdatatable that allows for regular expressions.

I currently hardcode the reshaping process, by building a list of dataframes, then rbind or cbind as the case may be.

Note : rbind does not accept a generator expression, only lists.
dt.rbind([df[:,f[0].extend({"var":name, "val":f[name]})] for name in df.names[1:]])

Thanks!

[aniket328]

I am working on this issue, kindly assign it to me, will be creating PR in few days.

[danijak]

I am working with R. I want to contribute to this task.

[oleksiyskononenko]

@aniket328 I've assigned this issue to you.

@danijak Please coordinate with @aniket328 who seems to work on this issue already.

Thanks you both for your contributions!

[aniket328]

Sure @danijak, let's collaborate. :)

[st-pasha]

Hey @aniket328, @danijak -- are you coming from GSoC by any chance?

[danijak]

@st-pasha, I am GSoc'2021 Aspirant. I am looking to contribute in this issue

[aniket328]

Yes @st-pasha , I will be submitting a proposal for working in the R-Project for GSoC 2021

[danijak]

@aniket328 I've assigned this issue to you.

@danijak Please coordinate with @aniket328 who seems to work on this issue already.
Thanks you both for your contributions!

Thanks @oleksiyskononenko, I will check other issues as well. If there are any urgent issues to be resolved please do tell me.

[theadityasam]

Hey @st-pasha @samukweku @oleksiyskononenko
I would love to work on this issue for the summer of 2021. I've experience with the data.table R package and have myself used melt extensively. This is the link to the easy tests demonstrating my familiarity with the data.table R package.

[oleksiyskononenko]

Dear @theadityasam, it seems that there are already two people working on it — see comments above.

[theadityasam]

Will try my hands on the issue in my own fork meanwhile since I don't see any development yet.