Pandas：文件读取、存储【读取：read_()、写入：to_()】【文件类型：csv、excel、json、HDF5】

喜欢ヅ旅行 2023-09-29 09:40 15阅读 0赞

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

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTMyNTA4NjE_size_16_color_FFFFFF_t_70_pic_center]

### 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'])
    
    			open	close
    2018-02-27	23.53	24.16
    2018-02-26	22.80	23.53
    2018-02-23	22.88	22.82
    2018-02-22	22.25	22.28
    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

# 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: 0	open
    0	2018-02-27	23.53
    1	2018-02-26	22.80
    2	2018-02-23	22.88
    3	2018-02-22	22.25
    4	2018-02-14	21.49
    5	2018-02-13	21.40
    6	2018-02-12	20.70
    7	2018-02-09	21.20
    8	2018-02-08	21.79
    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。

# 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

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTMyNTA4NjE_size_16_color_FFFFFF_t_70_pic_center 1]

需要安装安装tables模块避免不能读取HDF5文件

pip install tables

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTMyNTA4NjE_size_16_color_FFFFFF_t_70_pic_center 2]

*  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：

{"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}

*  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：

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTMyNTA4NjE_size_16_color_FFFFFF_t_70_pic_center 3]

#### 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:\/\/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

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

结果

{"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}...

### 4 小结 ###

*  pandas的CSV、HDF5、JSON文件的读取【知道】
    
     *  对象.read\_\*\*()
     *  对象.to\_\*\*()

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