rlucas.net: The Next Generation

Perhaps you are data munging in Python, using “pandas”, and you attempt to use DataFrame.merge() in order to put two DataFrames together.

“cannot join with no level specified and no overlapping names”

This happens when you have two DataFrames with one having a MultiIndex type, which *could* play nice together (e.g. you have “year, month” on the left, and “year” on the right, *but do not have names set.*

You’ll need to explicitly set names with

leftdf.index.levels[0].name = “onename”
leftdf.index.levels[1].name = “twoname”
rightdf.index.levels[0].name = “onename”

Alternatively, you can make it work if you reindex the right-hand side by the left hand side:

rightdf2 = rightdf.reindex(index=leftdf.index, level=0) ## NOTE Assignment, does not modify rightdf in-place

This entry was posted on Thursday, July 3rd, 2014 at 3:09 pm and is filed under bugfix. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.