Pandas 库学习
声明：学习内容来自 \(Kaggle\) 的官方教程
Course 1: Creating, Reading and Writing
1.1 DataFrame 创建
pd.DataFrame({'Bob': ['I liked it.', 'It was awful.'], 'Sue': ['Pretty good.', 'Bland.']}, index=['Product A', 'Product B'])
| Bob | Sue | |
|---|---|---|
| Product A | I liked it. | Pretty good. |
| Product B | It was awful. | Bland. |
1.2 Series 创建
pd.Series([30, 35, 40], index=['2015 Sales', '2016 Sales', '2017 Sales'], name='Product A')
2015 Sales 30
2016 Sales 35
2017 Sales 40
Name: Product A, dtype: int64
1.3 read_csv 读文件
wine_reviews = pd.read_csv("../input/wine-reviews/winemag-data-130k-v2.csv", index_col=0)
#index_col=0 使第一列识别为索引
1.4 基本访问操作
wine_reviews.shape #shape 查询数据集大小
wine_reviews.head()#head 查询前五条
1.5 to_csv 存文件
animals.to_csv("cows_and_goats.csv")
Course 2: Indexing, Selecting & Assigning
图：数据集（部分）
2.1 先列后行的截取：索引名
review.country
reviews['country']
0 Italy
1 Portugal...
129969 France
129970 France
Name: country, Length: 129971, dtype: object
reviews['country'][0]
'Italy'
2.2 先行后列的截取：iloc
reviews.iloc[0] #单参数取行
country Italy
description Aromas include tropical fruit, broom, brimston......
variety White Blend
winery Nicosia
Name: 0, Length: 13, dtype: object
reviews.iloc[:, 0]
0 Italy
1 Portugal...
129969 France
129970 France
Name: country, Length: 129971, dtype: object
reviews.iloc[:3, 0]
0 Italy
1 Portugal
2 US
Name: country, dtype: object
reviews.iloc[1:3, 0]
1 Portugal
2 US
Name: country, dtype: object
reviews.iloc[[0, 1, 2], 0]
0 Italy
1 Portugal
2 US
Name: country, dtype: object
reviews.iloc[-5:]
2.3 先行后列的截取：loc
loc 的截取，行参数基于条目序号，列参数基于索引名称
需要注意的是，loc 是包容性的索引方式，与标准库的索引方案不同
reviews.loc[0, 'country']
'Italy'
reviews.loc[:, ['taster_name', 'taster_twitter_handle', 'points']]
2.4 set_index 顶部添加行
reviews.set_index("title")
2.5 条件选择
reviews.country == 'Italy'
0 True
1 False...
129969 False
129970 False
Name: country, Length: 129971, dtype: bool
reviews.loc[reviews.country == 'Italy']reviews.loc[(reviews.country == 'Italy') & (reviews.points >= 90)]reviews.loc[(reviews.country == 'Italy') | (reviews.points >= 90)]reviews.loc[reviews.country.isin(['Italy', 'France'])]reviews.loc[reviews.price.notnull()]
2.6 赋值
reviews['critic'] = 'everyone'reviews['index_backwards'] = range(len(reviews), 0, -1)