What is the difference between join and merge in Pandas?

Michael Zippo

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Suppose I have two DataFrames like so:

left = pd.DataFrame({"key1": ["foo", "bar"], "lval": [1, 2]})

right = pd.DataFrame({"key2": ["foo", "bar"], "rval": [4, 5]})

I want to merge them, so I try something like this:

pd.merge(left, right, left_on="key1", right_on="key2")

And I"m happy

    key1    lval    key2    rval
0   foo     1       foo     4
1   bar     2       bar     5

But I"m trying to use the join method, which I"ve been lead to believe is pretty similar.

left.join(right, on=["key1", "key2"])

And I get this:

//anaconda/lib/python2.7/site-packages/pandas/tools/merge.pyc in _validate_specification(self)
    406             if self.right_index:
    407                 if not ((len(self.left_on) == self.right.index.nlevels)):
--> 408                     raise AssertionError()
    409                 self.right_on = [None] * n
    410         elif self.right_on is not None:

AssertionError:

What am I missing?

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Frank Krasiko

Singapore | 2023-03-21

Simply put and clear. Thank you for sharing. What is the difference between join and merge in Pandas? and other issues with re Python module was always my weak point 😁. I just hope that will not emerge anymore

Frank Innsbruck

Berlin | 2023-03-21

Simply put and clear. Thank you for sharing. What is the difference between join and merge in Pandas? and other issues with code Python module was always my weak point 😁. Checked yesterday, it works!

Olivia Zelotti

Milan | 2023-03-21

Maybe there are another answers? What What is the difference between join and merge in Pandas? exactly means?. Will get back tomorrow with feedback