Selecting columns

Introduction to Data Science in Python

Hillary Green-Lerman

Lead Data Scientist, Looker

Why select columns?

Use in a calculation
```
credit_records.price.sum()
```

Plot data

plt.plot(ransom['letter'], ransom['frequency'])

Columns names are strings

print(credit_records.head())

            suspect         location              date         item  price
0    Kirstine Smith   Groceries R Us   January 6, 2018     broccoli   1.25
1      Gertrude Cox  Petroleum Plaza   January 6, 2018  fizzy drink   1.90
2  Fred Frequentist   Groceries R Us   January 6, 2018     broccoli   1.25
3      Gertrude Cox   Groceries R Us  January 12, 2018     broccoli   1.25
4    Kirstine Smith    Clothing Club   January 9, 2018        shirt  14.25

'suspect'
'location'
'date'
'item'
'price'

Selecting with brackets and string

suspect = credit_records['suspect']

print(suspect)

0            Kirstine Smith
1              Gertrude Cox
2          Fred Frequentist
3              Gertrude Cox
4            Kirstine Smith
5              Gertrude Cox
...
99             Gertrude Cox
100        Fred Frequentist
101            Gertrude Cox
102          Kirstine Smith
103    Ronald Aylmer Fisher

Selecting with a dot

price = credit_records.price

print(price)

0       1.25
1       1.90
2       1.25
3       1.25
4      14.25
5       3.95
...
99     14.25
100    12.05
101    20.15
102     3.95
103     2.05

Common mistakes in column selection

Use brackets and string for column names with spaces or special characters (-, ?, etc.)

police_report['Is Golden Retriever?']

NOT

police_report.Is Golden Retriever?

Object `Retriever` not found.

Common mistakes in column selection

When using brackets and string, don't forget the quotes around the column name!

credit_report['location']

NOT

credit_report[location]

Object `location` not found.

Common mistakes in column selection

Brackets, not parentheses

credit_report['location']

NOT

credit_report('location')

----------------------------------------------------------------------
TypeError  Traceback (most recent call last)
<ipython-input-5-aabdb8981438> in <module>()
----> 1 credit_report('location')

TypeError: 'DataFrame' object is not callable

Let's practice!

Introduction to Data Science in Python