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I know this question is quite trivial, but this is my first day of using pandas, so please at least post a link to the document which I should read.

Basically, I don't know how to count the number of items of each column. Suppose I have a data frame like this:

df = pandas.DataFrame({ "Grade": [1, 2, 1, 1, 2, 1, 2, 2, 1], "Major": ["Science", "Art", "Engineering", "Science", "Science", "Science", "Science", "Engineering", "Engineering"]})

I expect the following result:

Grade Major Number 1 Science 3 1 Engineering 2 1 Art 0 2 Science 2 2 Engineering 1 2 Art 1
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I think you need groupby with aggregating size:

print (df.groupby(['Grade','Major']).size().reset_index(name='Number')) Grade Major Number 0 1 Engineering 2 1 1 Science 3 2 2 Art 1 3 2 Engineering 1 4 2 Science 2

If need add missing values per group, add unstack with stack:

print (df.groupby(['Grade','Major']) .size() .unstack(fill_value=0) .stack() .reset_index(name='Number')) Grade Major Number 0 1 Art 0 1 1 Engineering 2 2 1 Science 3 3 2 Art 1 4 2 Engineering 1 5 2 Science 2
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