学习目标

  • 目标
    • 了解Pandas的几种文件读取存储操作
    • 应用CSV方式、HDF方式和json方式实现文件的读取和存储

我们的数据大部分存在于文件当中，所以pandas会支持复杂的IO操作，pandas的API支持众多的文件格式，如CSV、SQL、XLS、JSON、HDF5。

注：最常用的HDF5和CSV文件

读取存储.png

1 CSV

1.1 read_csv

  • pandas.read_csv(filepath_or_buffer, sep =’,’, usecols )
    • filepath_or_buffer:文件路径
    • sep :分隔符，默认用”,”隔开
    • usecols:指定读取的列名，列表形式

  • 举例：读取之前的股票的数据

    1. # 读取文件,并且指定只获取'open', 'close'指标
    2. data = pd.read_csv("./data/stock_day.csv", usecols=['open', 'close'])
    4.           open    close
    5. 2018-02-27    23.53    24.16
    6. 2018-02-26    22.80    23.53
    7. 2018-02-23    22.88    22.82
    8. 2018-02-22    22.25    22.28
    9. 2018-02-14    21.49    21.92

    1.2 to_csv

  • DataFrame.to_csv(path_or_buf=None, sep=’, ’, columns=None, header=True, index=True, mode=’w’, encoding=None)

    • path_or_buf :文件路径
    • sep :分隔符，默认用”,”隔开
    • columns :选择需要的列索引
    • header :boolean or list of string, default True,是否写进列索引值
    • index:是否写进行索引
    • mode:’w’：重写, ‘a’ 追加

  • 举例：保存读取出来的股票数据

    • 保存’open’列的数据，然后读取查看结果

      1. # 选取10行数据保存,便于观察数据
      2. data[:10].to_csv("./data/test.csv", columns=['open'])
      1. # 读取，查看结果
      2. pd.read_csv("./data/test.csv")
      4. Unnamed: 0    open
      5. 0    2018-02-27    23.53
      6. 1    2018-02-26    22.80
      7. 2    2018-02-23    22.88
      8. 3    2018-02-22    22.25
      9. 4    2018-02-14    21.49
      10. 5    2018-02-13    21.40
      11. 6    2018-02-12    20.70
      12. 7    2018-02-09    21.20
      13. 8    2018-02-08    21.79
      14. 9    2018-02-07    22.69

      会发现将索引存入到文件当中，变成单独的一列数据。如果需要删除，可以指定index参数,删除原来的文件，重新保存一次。

      1. # index:存储不会讲索引值变成一列数据
      2. data[:10].to_csv("./data/test.csv", columns=['open'], index=False)

      2 HDF5

      2.1 read_hdf与to_hdf

      HDF5文件的读取和存储需要指定一个键，值为要存储的DataFrame

  • pandas.read_hdf(path_or_buf，key =None，** kwargs)从h5文件当中读取数据

    • path_or_buffer:文件路径
    • key:读取的键
    • return:Theselected object

  • DataFrame.tohdf(path_or_buf, _key, __kwargs)

    2.2 案例

  • 读取文件

    1. day_close = pd.read_hdf("./data/day_close.h5")

    如果读取的时候出现以下错误readh5.png
    需要安装安装tables模块避免不能读取HDF5文件

    1. pip install tables

    tables.png

  • 存储文件

    1. day_close.to_hdf("./data/test.h5", key="day_close")

    再次读取的时候, 需要指定键的名字

    1. new_close = pd.read_hdf("./data/test.h5", key="day_close")

    注意：优先选择使用HDF5文件存储

  • HDF5在存储的时候支持压缩，使用的方式是blosc，这个是速度最快的也是pandas默认支持的

  • 使用压缩可以提磁盘利用率，节省空间

  • HDF5还是跨平台的，可以轻松迁移到hadoop 上面

    3 JSON

    JSON是我们常用的一种数据交换格式，前面在前后端的交互经常用到，也会在存储的时候选择这种格式。所以我们需要知道Pandas如何进行读取和存储JSON格式。

    3.1 read_json

  • pandas.read_json(path_or_buf=None, orient=None, typ=’frame’, lines=False)

    • 将JSON格式准换成默认的Pandas DataFrame格式
    • orient : string,Indication of expected JSON string format.
      • ‘split’ : dict like {index -> [index], columns -> [columns], data -> [values]}
        • split 将索引总结到索引，列名到列名，数据到数据。将三部分都分开了
      • ‘records’ : list like [{column -> value}, … , {column -> value}]
        • records 以columns：values的形式输出
      • ‘index’ : dict like {index -> {column -> value}}
        • index 以index：{columns：values}…的形式输出
      • ‘columns’ : dict like {column -> {index -> value}},默认该格式
        • colums 以columns:{index:values}的形式输出
      • ‘values’ : just the values array
        • values 直接输出值
    • lines : boolean, default False
      • 按照每行读取json对象
    • typ : default ‘frame’， 指定转换成的对象类型series或者dataframe

      3.2 read_josn 案例

  • 数据介绍

这里使用一个新闻标题讽刺数据集，格式为json。is_sarcastic：1讽刺的，否则为0；headline：新闻报道的标题；article_link：链接到原始新闻文章。存储格式为：

  1. {"article_link": "https://www.huffingtonpost.com/entry/versace-black-code_us_5861fbefe4b0de3a08f600d5", "headline": "former versace store clerk sues over secret 'black code' for minority shoppers", "is_sarcastic": 0}
  2. {"article_link": "https://www.huffingtonpost.com/entry/roseanne-revival-review_us_5ab3a497e4b054d118e04365", "headline": "the 'roseanne' revival catches up to our thorny political mood, for better and worse", "is_sarcastic": 0}
  • 读取

orient指定存储的json格式，lines指定按照行去变成一个样本

  1. json_read = pd.read_json("./data/Sarcasm_Headlines_Dataset.json", orient="records", lines=True)

结果为：新闻标题讽刺读取.png

3.3 to_json

  • DataFrame.tojson(_path_or_buf=None, orient=None, lines=False)

    • 将Pandas 对象存储为json格式
    • path_or_buf=None：文件地址
    • orient:存储的json形式，{‘split’,’records’,’index’,’columns’,’values’}
    • lines:一个对象存储为一行

      3.4 案例

  • 存储文件

    1. json_read.to_json("./data/test.json", orient='records')

    结果

    1. [{"article_link":"https:\/\/www.huffingtonpost.com\/entry\/versace-black-code_us_5861fbefe4b0de3a08f600d5","headline":"former versace store clerk sues over secret 'black code' for minority shoppers","is_sarcastic":0},{"article_link":"https:\/\/www.huffingtonpost.com\/entry\/roseanne-revival-review_us_5ab3a497e4b054d118e04365","headline":"the 'roseanne' revival catches up to our thorny political mood, for better and worse","is_sarcastic":0},{"article_link":"https:\/\/local.theonion.com\/mom-starting-to-fear-son-s-web-series-closest-thing-she-1819576697","headline":"mom starting to fear son's web series closest thing she will have to grandchild","is_sarcastic":1},{"article_link":"https:\/\/politics.theonion.com\/boehner-just-wants-wife-to-listen-not-come-up-with-alt-1819574302","headline":"boehner just wants wife to listen, not come up with alternative debt-reduction ideas","is_sarcastic":1},{"article_link":"https:\/\/www.huffingtonpost.com\/entry\/jk-rowling-wishes-snape-happy-birthday_us_569117c4e4b0cad15e64fdcb","headline":"j.k. rowling wishes snape happy birthday in the most magical way","is_sarcastic":0},{"article_link":"https:\/\/www.huffingtonpost.com\/entry\/advancing-the-worlds-women_b_6810038.html","headline":"advancing the world's women","is_sarcastic":0},....]

  • 修改lines参数为True

    1. json_read.to_json("./data/test.json", orient='records', lines=True)

    结果

    1. {"article_link":"https:\/\/www.huffingtonpost.com\/entry\/versace-black-code_us_5861fbefe4b0de3a08f600d5","headline":"former versace store clerk sues over secret 'black code' for minority shoppers","is_sarcastic":0}
    2. {"article_link":"https:\/\/www.huffingtonpost.com\/entry\/roseanne-revival-review_us_5ab3a497e4b054d118e04365","headline":"the 'roseanne' revival catches up to our thorny political mood, for better and worse","is_sarcastic":0}
    3. {"article_link":"https:\/\/local.theonion.com\/mom-starting-to-fear-son-s-web-series-closest-thing-she-1819576697","headline":"mom starting to fear son's web series closest thing she will have to grandchild","is_sarcastic":1}
    4. {"article_link":"https:\/\/politics.theonion.com\/boehner-just-wants-wife-to-listen-not-come-up-with-alt-1819574302","headline":"boehner just wants wife to listen, not come up with alternative debt-reduction ideas","is_sarcastic":1}
    5. {"article_link":"https:\/\/www.huffingtonpost.com\/entry\/jk-rowling-wishes-snape-happy-birthday_us_569117c4e4b0cad15e64fdcb","headline":"j.k. rowling wishes snape happy birthday in the most magical way","is_sarcastic":0}...

    4 小结

  • pandas的CSV、HDF5、JSON文件的读取【知道】

    • 对象.read_**()
    • 对象.to_**()