python pandas dataframe merge

Question

I want to merge some dataframe from csv files using for loop in python. But the result is empty. Why is that so? Here is my code.

result = pandas.DataFrame(columns = ['col_A', 'col_B'])
for i in range(0, 5):
    #col_A is integer for numbering, col_B is float in range 0 to 1
    temp = pandas.DataFrame([[0, 0.5132443], [1, 0.12436421], [2, 0.12341162]], columns = ['col_A', 'col_B'])
    result.merge(temp)
print(result) #result is empty dataframe

Have you verified temp is actually assigned to a dataframe after running? — Andrew L
– Andrew L, Commented May 27, 2017 at 14:20
Please read how to make good reproducible pandas examples and edit your post correspondingly. — MaxU - stand with Ukraine
– MaxU - stand with Ukraine, Commented May 27, 2017 at 16:41
yes, temp is actually assigned and remains after for loop. And code is run without any error — Noh Jongcheol
– Noh Jongcheol, Commented May 28, 2017 at 2:50
The challenge I am having understanding this, is that result is not defined, and thus result.merge should cause an error. Where is result defined? — Stephen Rauch
– Stephen Rauch ♦, Commented May 28, 2017 at 3:00

Stephen Rauch · Accepted Answer · 2017-05-27 14:07:13Z

1

You need to store the result of the merge:

result = result.merge(temp)

From the (DOCS

Returns:

merged : DataFrame

The output type will the be same as ‘left’, if it is a subclass of DataFrame.

answered May 27, 2017 at 14:07

Stephen Rauch♦

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