我对nunique有个问题,它被一个空的groupby调用,它以一个错误结束
>df
Empty DataFrame
Columns: [A, B]
Index: []
>df.groupby(['A'])['B'].nunique()
IndexError: index 0 is out of bounds for axis 0 with size 0
我想添加一个简单的检查,如果groupby是空的,只返回一个空序列。你知道吗
我在python portable中更改了nunique的def,并在那里添加了一个有效的检查:
def nunique(self, dropna=True):
""" Returns number of unique elements in the group """
ids, _, _ = self.grouper.group_info
val = self.obj.get_values()
try:
sorter = np.lexsort((val, ids))
except TypeError: # catches object dtypes
assert val.dtype == object, \
'val.dtype must be object, got %s' % val.dtype
val, _ = algos.factorize(val, sort=False)
sorter = np.lexsort((val, ids))
isnull = lambda a: a == -1
else:
isnull = com.isnull
ids, val = ids[sorter], val[sorter]
if ids.size == 0: ######Thats what I've added
return Series(ids,index=self.grouper.result_index,name=self.name)
# group boundaries are where group ids change
# unique observations are where sorted values change
idx = np.r_[0, 1 + np.nonzero(ids[1:] != ids[:-1])[0]]
inc = np.r_[1, val[1:] != val[:-1]]
# 1st item of each group is a new unique observation
mask = isnull(val)
if dropna:
inc[idx] = 1
inc[mask] = 0
else:
inc[mask & np.r_[False, mask[:-1]]] = 0
inc[idx] = 1
out = np.add.reduceat(inc, idx).astype('int64', copy=False)
res = out if ids[0] != -1 else out[1:]
ri = self.grouper.result_index
# we might have duplications among the bins
if len(res) != len(ri):
res, out = np.zeros(len(ri), dtype=out.dtype), res
res[ids] = out
return Series(res,
index=ri,
name=self.name)
问题是我不能改变portable本身,我需要重写nunique或者添加一个包装函数,当groupby(…).nunique()被调用时,这个包装函数将被调用。 我在网上看了看,但什么也找不到(也不懂)。 抱歉,如果这可能是一个简单的问题,但我是一个新手程序员,所以请对我放松:)
谢谢你
如何使用apply函数添加一个条件来检查组的长度?你知道吗
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