python - 将数据帧输出到 json 数组

Question

想知道有没有更高效的方法来做下面的操作。

# transforms datetime into timestamp in seconds
t = df.index.values.astype(np.int64) // 10**6

return jsonify(np.c_[t, df.open, df.high, df.low, df.close, df.volume].tolist())

其中 df 是一个包含日期索引的数据框，并且至少(但不仅限于)以下属性:open、high，低，关闭，音量。然后，我使用 flask 的 jsonify 将新创建的数组输出为 JSON。上面的代码有效，但对我来说，关于如何让它更好/更高效的任何想法，它看起来都非常低效。

Answer 1

你可以使用to_json()方法:

In [88]: import pandas_datareader.data as web

In [89]: apl = web.get_data_yahoo('AAPL', '2016-07-05', '2016-07-07')

In [90]: apl
Out[90]:
                 Open       High        Low      Close    Volume  Adj Close
Date
2016-07-05  95.389999  95.400002  94.459999  94.989998  27705200  94.989998
2016-07-06  94.599998  95.660004  94.370003  95.529999  30949100  95.529999
2016-07-07  95.699997  96.500000  95.620003  95.940002  25139600  95.940002

我将使用 json.dumps(..., indent=2) 以使其更好/可读:

In [91]: import json

orient='index'

In [98]: print(json.dumps(json.loads(apl.to_json(orient='index')), indent=2))
{
  "1467849600000": {
    "Close": 95.940002,
    "High": 96.5,
    "Open": 95.699997,
    "Adj Close": 95.940002,
    "Volume": 25139600,
    "Low": 95.620003
  },
  "1467676800000": {
    "Close": 94.989998,
    "High": 95.400002,
    "Open": 95.389999,
    "Adj Close": 94.989998,
    "Volume": 27705200,
    "Low": 94.459999
  },
  "1467763200000": {
    "Close": 95.529999,
    "High": 95.660004,
    "Open": 94.599998,
    "Adj Close": 95.529999,
    "Volume": 30949100,
    "Low": 94.370003
  }
}

orient='records'(重置索引以使列 Date 可见):

In [99]: print(json.dumps(json.loads(apl.reset_index().to_json(orient='records')), indent=2))
[
  {
    "Close": 94.989998,
    "High": 95.400002,
    "Open": 95.389999,
    "Adj Close": 94.989998,
    "Volume": 27705200,
    "Date": 1467676800000,
    "Low": 94.459999
  },
  {
    "Close": 95.529999,
    "High": 95.660004,
    "Open": 94.599998,
    "Adj Close": 95.529999,
    "Volume": 30949100,
    "Date": 1467763200000,
    "Low": 94.370003
  },
  {
    "Close": 95.940002,
    "High": 96.5,
    "Open": 95.699997,
    "Adj Close": 95.940002,
    "Volume": 25139600,
    "Date": 1467849600000,
    "Low": 95.620003
  }
]

您可以使用以下 to_json() 参数:

date_format : {‘epoch’, ‘iso’}

Type of date conversion. epoch = epoch milliseconds, iso` = ISO8601, default is epoch.

date_unit : string, default ‘ms’ (milliseconds)

The time unit to encode to, governs timestamp and ISO8601 precision.One of ‘s’, ‘ms’, ‘us’, ‘ns’ for second, millisecond, microsecond, andnanosecond respectively.

orient : string

The format of the JSON string

• split : dict like {index -> [index], columns -> [columns], data -> [values]}
• records : list like [{column -> value}, ... , {column -> value}]
• index : dict like {index -> {column -> value}}
• columns : dict like {column -> {index -> value}} values : just the values array