python - 如何通过索引列表从 dask 数据框中选择数据？

Question

我想根据索引列表从 dask 数据框中选择行。我怎样才能做到这一点？

示例： 假设我有以下 dask 数据框。

dict_ = {'A':[1,2,3,4,5,6,7], 'B':[2,3,4,5,6,7,8], 'index':['x1', 'a2', 'x3', 'c4', 'x5', 'y6', 'x7']}
pdf = pd.DataFrame(dict_)
pdf = pdf.set_index('index')
ddf = dask.dataframe.from_pandas(pdf, npartitions = 2)

此外，我有一个我感兴趣的索引列表，例如

indices_i_want_to_select = ['x1','x3', 'y6']

由此，我想生成一个仅包含在indices_i_want_to_select

Answer 1

编辑：dask 现在支持 loc 列表：

ddf_selected = ddf.loc[indices_i_want_to_select]

以下应该仍然有效，但不再需要：

import pandas as pd
import dask.dataframe as dd

#generate example dataframe
pdf = pd.DataFrame(dict(A = [1,2,3,4,5], B = [6,7,8,9,0]), index=['i1', 'i2', 'i3', 4, 5])
ddf = dd.from_pandas(pdf, npartitions = 2)

#list of indices I want to select
l = ['i1', 4, 5]

#generate new dask dataframe containing only the specified indices
ddf_selected = ddf.map_partitions(lambda x: x[x.index.isin(l)], meta = ddf.dtypes)

Answer 2

由于混合索引类型，使用dask版本“1.2.0”会导致错误。在任何情况下都有一个选项可以使用loc。

import pandas as pd
import dask.dataframe as dd

#generate example dataframe
pdf = pd.DataFrame(dict(A = [1,2,3,4,5], B = [6,7,8,9,0]), index=['i1', 'i2', 'i3', '4', '5'])
ddf = dd.from_pandas(pdf, npartitions = 2,)

# #list of indices I want to select
l = ['i1', '4', '5']

# #generate new dask dataframe containing only the specified indices
# ddf_selected = ddf.map_partitions(lambda x: x[x.index.isin(l)], meta = ddf.dtypes)
ddf_selected = ddf.loc[l]
ddf_selected.head()