python - 使用 pandas read_csv 缺少数据

Question

我正在尝试读取 csv 文件，其中某些行可能缺少数据 block 。

当您指定 dtype 时，这似乎会导致 pandas read_csv 函数出现问题。问题似乎是，为了从 str 转换为 dtype 指定的任何内容，pandas 只是尝试直接转换它。因此，如果缺少某些东西，事情就会崩溃。

后面是一个 MWE(该 MWE 使用 StringIO 代替真实文件；但是，使用真实文件时也会出现此问题)

import pandas as pd
import numpy as np
import io

datfile = io.StringIO("12 23 43| | 37| 12.23| 71.3\n12 23 55|X|   |      | 72.3")

names = ['id', 'flag', 'number', 'data', 'data2']
dtypes = [np.str, np.str, np.int, np.float, np.float]

dform = {name: dtypes[ind] for ind, name in enumerate(names)}

colconverters = {0: lambda s: s.strip(), 1: lambda s: s.strip()}

df = pd.read_table(datfile, sep='|', dtype=dform, converters=colconverters, header=None,
                   index_col=0, names=names, na_values=' ')

运行时出现的错误是

Traceback (most recent call last):
  File "pandas/parser.pyx", line 1084, in pandas.parser.TextReader._convert_tokens (pandas/parser.c:12580)
TypeError: Cannot cast array from dtype('O') to dtype('int64') according to the rule 'safe'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/aliounis/Repos/stellarpy/source/mwe.py", line 15, in <module>
    index_col=0, names=names, na_values=' ')
  File "/usr/local/lib/python3.5/site-packages/pandas/io/parsers.py", line 562, in parser_f
    return _read(filepath_or_buffer, kwds)
  File "/usr/local/lib/python3.5/site-packages/pandas/io/parsers.py", line 325, in _read
    return parser.read()
  File "/usr/local/lib/python3.5/site-packages/pandas/io/parsers.py", line 815, in read
    ret = self._engine.read(nrows)
  File "/usr/local/lib/python3.5/site-packages/pandas/io/parsers.py", line 1314, in read
    data = self._reader.read(nrows)
  File "pandas/parser.pyx", line 805, in pandas.parser.TextReader.read (pandas/parser.c:8748)
  File "pandas/parser.pyx", line 827, in pandas.parser.TextReader._read_low_memory (pandas/parser.c:9003)
  File "pandas/parser.pyx", line 904, in pandas.parser.TextReader._read_rows (pandas/parser.c:10022)
  File "pandas/parser.pyx", line 1011, in pandas.parser.TextReader._convert_column_data (pandas/parser.c:11397)
  File "pandas/parser.pyx", line 1090, in pandas.parser.TextReader._convert_tokens (pandas/parser.c:12656)
ValueError: invalid literal for int() with base 10: '   '

有什么办法可以解决这个问题吗？我浏览了文档，但没有看到任何看起来可以直接解决此解决方案的内容。这只是一个需要向 panda 报告的错误吗？

Answer 1

试试这个:

import pandas as pd
import numpy as np
import io

datfile = io.StringIO(u"12 23 43| | 37| 12.23| 71.3\n12 23 55|X|   |      | 72.3")

names  = ['id', 'flag', 'number', 'data', 'data2']
dtypes = [np.str, np.str, np.str, np.float, np.float] 
dform  = {name: dtypes[ind] for ind, name in enumerate(names)}

colconverters = {0: lambda s: s.strip(), 1: lambda s: s.strip()}

df     = pd.read_table(datfile, sep='|', dtype=dform, converters=colconverters, header=None, na_values=' ')
df.columns = names

编辑:导入后转换数据类型。

df["number"] = df["data"].astype('int')
df["data"]   = df["data"].astype('float')

您的数据混合了空格作为字符串和数字。

<class 'pandas.core.frame.DataFrame'>
RangeIndex: 2 entries, 0 to 1
Data columns (total 5 columns):
id        2 non-null object
flag      2 non-null object
number    2 non-null object
data      2 non-null object
data2     2 non-null float64
dtypes: float64(1), object(4)
memory usage: 152.0+ bytes

如果您查看data，它是np.float，但转换为对象，而data2是np.float > 直到出现空白，它也会变成对象。