List Comprehension Over Pandas Dataframe Rows

Tristan Fletcher

I can't understand why this snippet of code:

df = PA.DataFrame()
[df.append(aFunction(x)) for x in aPandaSeries]

does not give me the same DataFrame (df) as:

df = PA.DataFrame()
for x in xrange(len(aPandaSeries)):
        df = df.append(aFunction(aPandaSeries[x]))

I am trying to pythonise the second section by using the first section, but df has far fewer rows in the former than the latter.

Rainy

A couple of things...

  1. .append() method returns None. So df = df.append() will set df to None value.

  2. List comprehensions are useful to filter or process a list of values, so you generally wouldn't use .append() with a list comprehension. It makes more sense to rewrite the 2nd line in first snippet as:

for x in aPandaSeries: df.append(aFunction(x))

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