[英]Most frequent value using pandas.DataFrame.resample
I am using pandas.DataFrame.resample
to resample a grouped Pandas dataframe
with a timestamp index. 我正在使用pandas.DataFrame.resample
来重新采样带有时间戳索引的分组Pandas dataframe
。
In one of the columns, I would like to resample such that I select the most frequent value. 在其中一列中,我想重新采样,以便选择最常用的值。 At the moment, I am only having success using NumPy functions like np.max
or np.sum
etc. 目前,我只是成功使用np.max
或np.sum
等NumPy函数。
#generate test dataframe
data = np.random.randint(0,10,(366,2))
index = pd.date_range(start=pd.Timestamp('1-Dec-2012'), periods=366, unit='D')
test = pd.DataFrame(data, index=index)
#generate group array
group = np.random.randint(0,2,(366,))
#define how dictionary for resample
how_dict = {0: np.max, 1: np.min}
#perform grouping and resample
test.groupby(group).resample('48 h',how=how_dict)
The previous code works because I have used NumPy functions. 之前的代码有效,因为我使用了NumPy函数。 However, if I want to use resample by most frequent value, I am not sure. 但是,如果我想以最常见的价值使用重新采样,我不确定。 I try defining a custom function like 我尝试定义一个自定义函数
def frequent(x):
(value, counts) = np.unique(x, return_counts=True)
return value[counts.argmax()]
However, if I now do: 但是,如果我现在这样做:
how_dict = {0: np.max, 1: frequent}
I get an empty dataframe... 我得到一个空的数据帧......
df = test.groupby(group).resample('48 h',how=how_dict)
df.shape
Your resample period is too short, so when a group is empty on a period, your user function raise a ValueError not kindly caught by pandas . 您的重新采样周期太短,因此当一个组在一段时间内为空时,您的用户函数会引发一个不会被pandas捕获的ValueError。
But it works without empty groups, for example with regular groups: 但它没有空组,例如使用常规组:
In [8]: test.groupby(arange(366)%2).resample('48h',how=how_dict).head()
Out[8]:
0 1
0 2012-12-01 4 8
2012-12-03 0 3
2012-12-05 9 5
2012-12-07 3 4
2012-12-09 7 3
Or with bigger periods : 或者更长的时期:
In [9]: test.groupby(group).resample('122D',how=how_dict)
Out[9]:
0 1
0 2012-12-02 9 0
2013-04-03 9 0
2013-08-03 9 6
1 2012-12-01 9 3
2013-04-02 9 7
2013-08-02 9 1
EDIT 编辑
A workaround can be to manage the empty case : 解决方法可以是管理空案例:
def frequent(x):
if len(x)==0 : return -1
(value, counts) = np.unique(x, return_counts=True)
return value[counts.argmax()]
For 对于
In [11]: test.groupby(group).resample('48h',how=how_dict).head()
Out[11]:
0 1
0 2012-12-01 5 3
2012-12-03 3 4
2012-12-05 NaN -1
2012-12-07 5 0
2012-12-09 1 4
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