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Intro To Python and Pandas

Python is one of the most popular and fastest growing software languages used in data analytics today and there are many reasons for that. I will cover majority of the topics in this blog in Python and occasionally R.

For those who are completely new to Python and programming, I encourage you to check out Codeacademy and do their free Python course. It’s important to get a good feel for this language and understand some fundamental concepts like syntax, libraries, data structures etc. The course is very straight forward and suitable for all level.

pandas is a Python library (prewritten code for us to use) and is the bread & butter for data analysis. I’m assuming everyone that’s reading this used Excel or some sort of spreadsheet before. Pandas essentially stores data in a tabular format (rows and columns like a spreadsheet) with predefined functionalities to manipulate & analyze data. After learning about basic Python, I encourage you to check out this tutorial from Greg Reda on how to use pandas.

In this series of blog articles, I will instead focus on this Panda’s cheatsheet and additional common functionalities, walking through some examples and relating to how you would use it on a day to day task. Lets start with creating Series an DataFrames, getting some data and removing some data.

import pandas as pd

Creating Series and DataFrame

Lets first define a Series. A Series is simply a one dimensional array, kind of like your Excel spreadsheet but with one column.

pd.Series([3, -5, 7, 4])
0    3
1   -5
2    7
3    4
dtype: int64

The 0, 1, 2, 3 here is the index of the series. They are like the row #s in excel. We can also have predefined index labels for our Series. Lets label it a, b, c, d

s = pd.Series([3, -5, 7, 4], index=['a', 'b', 'c', 'd'])
a    3
b   -5
c    7
d    4
dtype: int64

DataFrame on the other hand is like a Series but two dimensional, so like your full Excel sheet instead of one column. There are many ways to create a DataFrame with your data, its quite flexible and up to you what is the easiest based on the data set you have.

#if your data is already in dictionary form
data = {'Country': ['Belgium', 'India', 'Brazil'],
        'Capital': ['Brussels', 'New Delhi', 'Brasília'],
        'Population': [11190846, 1303171035, 207847528]}
df = pd.DataFrame(data)
Capital Country Population
0 Brussels Belgium 11190846
1 New Delhi India 1303171035
2 Brasília Brazil 207847528

Or you could have some Series you already defined and want to put them together into a DataFrame. The NaN here means there is unknown value.

s1 = pd.Series([3, -5, 7, 4])
s2 = pd.Series([1, 3, 6])
        's1': s1,
        's2': s2})
s1 s2
0 3 1.0
1 -5 3.0
2 7 6.0
3 4 NaN

Retrieving Data

Remember previously your Series by default is indexed by number (0,1,2,3) and you also labeled the index. You can get information either way, using index number or your label

print s['a']
print s[0]

DataFrame is similar. Earlier we created a DataFrame with country information. We can get a column by specifying the column name

0    Belgium
1      India
2     Brazil
Name: Country, dtype: object

Or multiple columns

df[['Country', 'Capital']]
Country Capital
0 Belgium Brussels
1 India New Delhi
2 Brazil Brasília

And to select a range of rows, we use the : operator. It simply means select from this index value up to this index value. E.g. 0:2 means select row index 0 and 1

Capital Country Population
0 Brussels Belgium 11190846
1 New Delhi India 1303171035

Deleting Data

Sometimes we dont need all the data in our DataFrame or Series. Pandas provide a very convenient way of removing the data using the drop function

b   -5
c    7
d    4
dtype: int64
b   -5
c    7
dtype: int64

DataFrame has an extra parameter that you need to specif, axis. Axis = 0 means you are looking to remove a row. Axis = 1 means you want to remove a column.

df.drop('Capital', axis=1)
Country Population
0 Belgium 11190846
1 India 1303171035
2 Brazil 207847528
df.drop([1,2], axis=0)
Capital Country Population
0 Brussels Belgium 11190846

A very simple function in Python is the range function, which allows you to define a range of number range([start],[stop])

[0, 1]
Capital Country Population
2 Brasília Brazil 207847528

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