pandas pandas中`header = None`和`header = 0`的区别
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difference between `header = None` and `header = 0` in pandas
提问by Sarvagya Gupta
I was writing a code to read a csvfile using pandasand I saw some weird functioning of the package. My file has column names which I want to ignore, so I use header = 0or 'infer'instead of None. But I see something weird.
我正在编写一个代码来读取csv文件pandas，我看到了包的一些奇怪的功能。我的文件有我想忽略的列名，所以我使用header = 0或'infer'代替None. 但我看到了一些奇怪的东西。
When I use Noneand I want to get a specific column, I just need to do df[column_index]but when I use 0or 'infer', I need to do df.ix[:,column_index]to get the column otherwise, for df[column_index]I get the following error:
当我使用None并且我想获取特定列时，我只需要这样做，df[column_index]但是当我使用0or 时'infer'，我需要df.ix[:,column_index]否则获取列，因为df[column_index]我收到以下错误：
Traceback (most recent call last): File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 2525, in get_loc return self._engine.get_loc(key) File "pandas/_libs/index.pyx", line 117, in pandas._libs.index.IndexEngine.get_loc File "pandas/_libs/index.pyx", line 139, in pandas._libs.index.IndexEngine.get_loc File "pandas/_libs/hashtable_class_helper.pxi", line 1265, in pandas._libs.hashtable.PyObjectHashTable.get_item File "pandas/_libs/hashtable_class_helper.pxi", line 1273, in pandas._libs.hashtable.PyObjectHashTable.get_item KeyError: column_index
During handling of the above exception, another exception occurred:
Traceback (most recent call last): File "", line 1, in File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/frame.py", line 2139, in getitemreturn self._getitem_column(key) File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/frame.py", line 2146, in _getitem_column return self._get_item_cache(key) File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/generic.py", line 1842, in _get_item_cache values = self._data.get(item) File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/internals.py", line 3843, in get loc = self.items.get_loc(item) File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 2527, in get_loc return self._engine.get_loc(self._maybe_cast_indexer(key)) File "pandas/_libs/index.pyx", line 117, in pandas._libs.index.IndexEngine.get_loc File "pandas/_libs/index.pyx", line 139, in pandas._libs.index.IndexEngine.get_loc File "pandas/_libs/hashtable_class_helper.pxi", line 1265, in pandas._libs.hashtable.PyObjectHashTable.get_item File "pandas/_libs/hashtable_class_helper.pxi", line 1273, in pandas._libs.hashtable.PyObjectHashTable.get_item KeyError: column_index
回溯（最近一次通话）：文件“/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/indexes/base.py”，第 2525 行，在 get_loc 中返回 self. _engine.get_loc(key) 文件“pandas/_libs/index.pyx”，第 117 行，pandas._libs.index.IndexEngine.get_loc 文件“pandas/_libs/index.pyx”，第 139 行，pandas._libs.index .IndexEngine.get_loc 文件“pandas/_libs/hashtable_class_helper.pxi”，第 1265 行，pandas._libs.hashtable.PyObjectHashTable.get_item 文件“pandas/_libs/hashtable_class_helper.pxi”，第 1273 行，pandas._libs. .get_item KeyError: column_index
在处理上述异常的过程中，又发生了一个异常：
回溯（最近一次调用）：文件“”，第 1 行，在文件“/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/frame.py”，第 2139 行, 在getitem返回 self._getitem_column(key) 文件“/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/frame.py”，第 2146 行，在 _getitem_column 中 return self._get_item_cache(key ) 文件“/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/generic.py”，第 1842 行，_get_item_cache values = self._data.get(item) 文件“ /home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/internals.py”，第 3843 行，在 get loc = self.items.get_loc(item) 文件“/home/ sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/indexes/base.py”，第 2527 行，在 get_loc 中返回 self._engine.get_loc(self._maybe_cast_indexer(key)) 文件“ pandas/_libs/index.pyx”，第 117 行，在 pandas._libs.index.IndexEngine.get_loc 文件中“pandas/_libs/index.pyx”，第 139 行，在 pandas._libs.index.IndexEngine.get_loc 文件“pandas/_libs/hashtable_class_helper.pxi”，第 1265 行，在 pandas._libs.hashtable.PyObjectHashTable.get_item 文件“pandas/ _libs/hashtable_class_helper.pxi”，第 1273 行，在 pandas._libs.hashtable.PyObjectHashTable.get_item KeyError: column_index
Can someone help with this? Why is this happening?
有人可以帮忙吗？为什么会这样？
回答by jezrael
It looks like need 2 parameters - header=Noneand skiprows=1if want ignore original columns names for default RangeIndex.
它看起来像需要两个参数-header=None而skiprows=1如果想忽略默认原始列名RangeIndex。
Because if use only header=Nonein first row get original columns names.
因为如果仅header=None在第一行中使用，则获取原始列名。
And header=0read first row to columns names of DataFrame.
并将header=0第一行读取到DataFrame.
Sample:
样品：
import pandas as pd
temp=u"""a,b,c
1,2,3
4,5,6"""
#after testing replace 'pd.compat.StringIO(temp)' to 'filename.csv'
df = pd.read_csv(pd.compat.StringIO(temp), header=0)
print (df)
a b c
0 1 2 3
1 4 5 6
Selecting by position:
按职位选择：
print (df.iloc[:, 1])
0 2
1 5
Name: b, dtype: int64
Selecting by column name:
按列名选择：
print (df['b'])
0 2
1 5
Name: b, dtype: int64
There is no column name 1, so:
没有列名1，所以：
print (df[1]) KeyError: 1
打印 (df[1]) KeyError: 1
df = pd.read_csv(pd.compat.StringIO(temp), header=None)
print (df)
0 1 2
0 a b c
1 1 2 3
2 4 5 6
df = pd.read_csv(pd.compat.StringIO(temp), header=None, skiprows=1)
print (df)
0 1 2
0 1 2 3
1 4 5 6
print (df[1])
0 2
1 5
Name: 1, dtype: int64
回答by Muffler
The difference pops up when working with a dataframe with header, so lets say your DataFrame dfhas header!
使用带有标题的数据帧时会出现差异，所以假设您的 DataFramedf有标题！
header=Nonepandas automatically assign the first row ofdf(which is the actual column names) to the first row, hence your columns no longer have namesheader=0, pandas first deletes column names(header) and then assign new column names to them (only if you pass names = [........] while loading your file).read_csv( filepath, header = 0 , names = ['....' , '....' ...])
header=Nonepandas 自动将第一行df（即实际列名）分配给第一行，因此您的列不再有名称header=0，pandas 首先删除列名（标题），然后为它们分配新的列名（仅当您在加载文件时传递 names = [........] 时）。read_csv( filepath, header = 0 , names = ['....' , '....' ...])
hope it helps!
希望能帮助到你！
