我想使用 shift()
从上一个索引中摘取数据,在其中一列中提供的值Letter
是相同的。
import pandas as pd
df = pd.DataFrame(data=[['A', 'one'],
['A', 'two'],
['B', 'three'],
['B', 'four'],
['C', 'five']],
columns=['Letter', 'value'])
df['Previous Value'] = df.apply(lambda x : x['value'] if x['Letter'].shift(1) == x['Letter'] else "", axis=1)
print df
我遇到了错误:
AttributeError: ("'str' object has no attribute 'shift'", u'occurred at index 0')
所需的输出:
Letter value Previous Value
0 A one
1 A two one
2 B three
3 B four three
4 C five
在您的条件上使用where
,其中当前行使用shift
匹配上一行:
In [11]:
df = pd.DataFrame(data=[['A', 'one'],
['A', 'two'],
['B', 'three'],
['B', 'four'],
['C', 'five']],
columns=['Letter', 'value'])
df['Previous Value'] = df['value'].shift().where(df['Letter'].shift() == df['Letter'], '')
df
Out[11]:
Letter value Previous Value
0 A one
1 A two one
2 B three
3 B four three
4 C five
您试图将.shift()应用于给定行的给定列的值而不是系列。我会使用Groupby:
这样做In [6]: df['Previous letter'] = df.groupby('Letter').value.shift()
In [7]: df
Out[7]:
Letter value Previous letter
0 A one NaN
1 A two one
2 B three NaN
3 B four three
4 C five NaN