python-3.x - 访问 Pandas 数据框中的第一列

Question

如何访问此数据框中的第一列？如果我通过列名(“Group11...”)引用它，我会收到“不在索引中”的错误。

First Column

Answer 1

您指的是数据帧的索引。因此，如果您的数据框名为 df，您可以使用 df.index 访问索引。

否则，如果要引用为列，则需要先将其转为列，然后再使用pandas.DataFrame.reset_index .

可重现的例子:

这是一个可重现的示例，显示了访问索引的两种方法:

from StringIO import StringIO 
import pandas as pd 

data = """Group11.Primary.Phrase|count|num_cat
CP|4|4
DA|1|1
FW|7|7
"""

df = pd.read_csv(StringIO(data), sep="|", index_col=0)
print("here's how the dataframe looks like") 
print(df.head())

print("here's how to access the index") 
print(df.index)

print("if you want to turn the index values into a list")
print(list(df.index))

print("you can also reset_index as a column and access it") 
df = df.reset_index()
print(df["Group11.Primary.Phrase"])

运行上面的代码，得到以下输出:

here's how the dataframe looks like                        count  num_catGroup11.Primary.Phrase                CP                          4        4DA                          1        1FW                          7        7here's how to access the indexIndex([u'CP', u'DA', u'FW'], dtype='object', name=u'Group11.Primary.Phrase')if you want to turn the index values into a list['CP', 'DA', 'FW']you can also reset_index as a column and access it0    CP1    DA2    FWName: Group11.Primary.Phrase, dtype: object