大约有 43,200 项符合查询结果（耗时：0.0414秒） [XML]
Pandas count(distinct) equivalent
...()
Example:
In [2]: table
Out[2]:
CLIENTCODE YEARMONTH
0 1 201301
1 1 201301
2 2 201301
3 1 201302
4 2 201302
5 2 201302
6 3 201302
In [3]: table.groupby('YEARMONTH').CLIENTCODE.nunique()
Out[3...
Explicitly select items from a list or tuple
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Especially:
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Cost of len() function
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It's O(1) (constant time, not depending of actual length of the element - very fast) on every type you've mentioned, plus set and others such as array.array.
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Understanding exactly when a data.table is a reference to (vs a copy of) another data.table
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