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
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keep_default_na=False，这样读取到空字符串时读出的就是’'而不是nan了 举例：读取之前的股票的数据# 读取文件,并且指定只获取'open', 'close'指标data = pd.read_csv("./data/stock_day.csv", usecols=['open', 'close'])openclose-02-2723.5324.16-02-2622.8023.53-02-2322.8822.82-02-2222.2522.28-02-1421.4921.92
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# 选取10行数据保存,便于观察数据data[:10].to_csv("./data/test.csv", columns=['open'])
# 读取，查看结果pd.read_csv("./data/test.csv")Unnamed: 0open0-02-2723.531-02-2622.802-02-2322.883-02-2222.254-02-1421.495-02-1321.406-02-1220.707-02-0921.208-02-0821.799-02-0722.69
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。
# index:存储不会讲索引值变成一列数据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.to_hdf(path_or_buf,key, **kwargs)
2.2 案例
读取文件day_close = pd.read_hdf("./data/day_close.h5")
如果读取的时候出现以下错误
需要安装安装tables模块避免不能读取HDF5文件
pip install tables
存储文件
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
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dataframe3.2 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：
{"article_link": "/entry/versace-black-code_us_5861fbefe4b0de3a08f600d5", "headline": "former versace store clerk sues over secret 'black code' for minority shoppers", "is_sarcastic": 0}{"article_link": "/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
json_read = pd.read_json("./data/Sarcasm_Headlines_Dataset.json", orient="records", lines=True)
结果为：
3.3 to_json
DataFrame.to_json(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json_read.to_json("./data/test.json", orient='records')
结果
[{"article_link":"https:\/\/\/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:\/\/\/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:\/\/\/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:\/\/\/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:\/\/\/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:\/\/\/entry\/advancing-the-worlds-women_b_6810038.html","headline":"advancing the world's women","is_sarcastic":0},....]
修改lines参数为True
json_read.to_json("./data/test.json", orient='records', lines=True)
结果
{"article_link":"https:\/\/\/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:\/\/\/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:\/\/\/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:\/\/\/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:\/\/\/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}...
