Implement inner/outer joins for non-keyed frames

[jangorecki]

Creating issue so I can be notified when feature will be ready.
We can also discuss API related to this FR here.
pandas way

x.merge(y, how='inner', on='KEY')

data.table way

X[Y, on="KEY", nomatch=0L]

R data.frame way (also supported in data.table)

merge(X, Y, by="KEY", all=TRUE)

[st-pasha]

The API, as discussed in #1187, will be as follows:

X[:, :, join(Y, on="key", how="inner")]  # i.e. X.key == Y.key
X[:, :, join(Y, on=["xkey", "ykey"])]
X[:, :, join(Y, on=(f.xkey == g.ykey))]

The parameter how takes values inner, outer, left and right (same as in pandas), with "inner" being the default.

[anarchy89]

is there a way to do full outer join yet?

[oleksiyskononenko]

@anarchy89 Nope, for the moment datatable only supports left outer joins. The issue gets closed when this feature is implemented.