选择列

Python 数据科学入门

Hillary Green-Lerman

Lead Data Scientist, Looker

为何要选择列？

用于计算
```
credit_records.price.sum()
```

绘制数据

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

列名是字符串

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'

用方括号和字符串选择

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

用点号选择

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

选列常见错误

列名含空格或特殊字符（-、? 等）时，用方括号和字符串

police_report['Is Golden Retriever?']

不要这样

police_report.Is Golden Retriever?

未找到对象 `Retriever`。

选列常见错误

使用方括号和字符串时，列名务必加引号！

credit_report['location']

不要这样

credit_report[location]

未找到对象 `location`。

选列常见错误

用方括号，不是小括号

credit_report['location']

不要这样

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

Vamos praticar!

Python 数据科学入门