[英]Dask how to pivot DataFrame
我正在使用下面的代码,但在旋转 DataFrame 后出现错误:
数据框:
name day value time
0 MAC000002 2012-12-16 0.147 09:30:00
1 MAC000002 2012-12-16 0.110 10:00:00
2 MAC000002 2012-12-16 0.736 10:30:00
3 MAC000002 2012-12-16 0.404 11:00:00
4 MAC000003 2012-12-16 0.845 00:30:00
读入数据,并透视
ddf = dd.read_csv('data.csv')
#I added this but didnt fix the error below
ddf.index.name = 'index'
#dask requires string as category type
ddf['name'] = ddf['name'].astype('category')
ddf['name'] =ddf['name'].cat.as_known()
#pivot the table
df = ddf.pivot_table(columns='name', values='value', index='index')
df.head()
#KeyError: 'index'
预期结果(有或没有索引) - 将行转为列,无需任何值修改:
MAC000002 MAC000003 ...
0.147 0.845
0.110 ...
0.736 ...
0.404 ...
知道为什么我会收到KeyError 'index'
以及如何克服这个问题吗?
根据pivot_table
的文档, index
kwarg 的值应引用现有列,因此不应将 name 设置为索引,而是应创建具有所需索引值的列:
# ddf.index.name = 'index'
ddf['index'] = ddf.index
请注意,这假设索引是您真正要旋转的索引。
下面是一个可重现的片段:
data = """
| name | day | value | time
0 | MAC000002 | 2012-12-16| 0.147| 09:30:00
1 | MAC000002 | 2012-12-16| 0.110| 10:00:00
2 | MAC000002 | 2012-12-16| 0.736| 10:30:00
3 | MAC000002 | 2012-12-16| 0.404| 11:00:00
4 | MAC000003 | 2012-12-16| 0.845| 00:30:00
"""
import pandas as pd
from io import StringIO
df = pd.read_csv(StringIO(data), sep='|')
df.columns = [c.strip() for c in df.columns]
import dask.dataframe as dd
ddf = dd.from_pandas(df, npartitions=3)
ddf['index'] = ddf.index
#dask requires string as category type
ddf['name'] = ddf['name'].astype('category')
ddf['name'] =ddf['name'].cat.as_known()
ddf.pivot_table(columns='name', values='value', index='index').compute()
# name MAC000002 MAC000003
# index
# 0 0.147 NaN
# 1 0.110 NaN
# 2 0.736 NaN
# 3 0.404 NaN
# 4 NaN 0.845
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