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Today I learned about the fundamental pandas data type Series.

A picture of panda (the mammal) with the words "pandas" and "Series" written.
Background photo by Elena Loshina on Unsplash.

What is a pandas Series?

A Series is one of the fundamental data types in pandas and is a one-dimensional container for data. Series are also indexable, either through integer indices (like the list or tuple built-in types), or through arbitrary hashable labels.

To create a Series, you just give it an iterable with the data you want:

>>> import pandas as pd     
>>> pd.Series([10, 20])
0    10
1    20
dtype: int64
>>> pd.Series(range(3))  
0    0
1    1
2    2
dtype: int64

The output above shows two columns, where the first column gives the indices (consecutive non-negative integers by default), and the second column shows the data.

Series are printed vertically to align with the fact that typically Series contain related data that you can often imagine as a column in a table of data.

How to define the labels of a pandas Series?

If you want to change the labels associated with your data, you can use the argument index when creating a Series:

>>> s = pd.Series(range(3), index=["a", "b", "c"])
>>> s
a    0
b    1
c    2
dtype: int64
>>> s["b"]
1

That's the most straightforward way to do it. Probably, there are others!

Non-unique Series labels

On top of the ability to support arbitrary (hashable) values for the labels of its values, a Series does not need unique labels. When the labels are non-unique and you use a one of those labels to access the Series, you access all of the values associated with that label:

>>> s = pd.Series(range(3), index=["a", "b", "a"])
>>> s["a"]
a    0
a    2
dtype: int64

Contrast this with the way the built-in dictionaries work:

>>> d = {"a": 0, "b": 1, "a": 2}
>>> d
{'a': 2, 'b': 1}
>>> d["a"]
2

Notice how the key "a" is only associated with the value 2 because keys in dictionaries must be unique.

That's it for now! Stay tuned and I'll see you around!

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