I want to create a new named column in a Pandas dataframe, insert first value into it, and then add another values to the same column:
Something like:
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import pandas2
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df = pandas.DataFrame()4
df['New column'].append('a')5
df['New column'].append('b')6
df['New column'].append('c')7
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etc.9
How do I do that?
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Answer
Dont do it, because it’s slow:
- updating an empty frame a-single-row-at-a-time. I have seen this method used WAY too much. It is by far the slowest. It is probably common place (and reasonably fast for some python structures), but a DataFrame does a fair number of checks on indexing, so this will always be very slow to update a row at a time. Much better to create new structures and concat.
Better to create a list of data and create DataFrame by contructor:
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vals = ['a','b','c']2
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df = pandas.DataFrame({'New column':vals})4