pandas 用给定分组的平均值替换nan [英] Pandas replace nan with mean value for a given grouping
问题描述
我有一个很大的数据集,格式为:
I have a large dataset of the form:
period_id gic_subindustry_id operating_mgn_fym5 operating_mgn_fym4 317 201509 25101010 13.348150 11.745965
682 201509 20101010 10.228725 10.473917
903 201509 20101010 NaN 17.700966
1057 201509 50101010 27.858305 28.378040
1222 201509 25502020 15.598956 11.658813
2195 201508 25502020 27.688324 22.969760
2439 201508 45202020 NaN 27.145216
2946 201508 45102020 17.956425 18.327724
实际上,在过去25年中,我每年都有成千上万个值,并且有多(10+)列.
In practice, I have thousands of values for each year going back 25 years, and multiple (10+) columns.
我正在尝试将该时间段内的NaN值替换为gic_industry_id中位数/平均值.
I am trying to replace the NaN values with the gic_industry_id median/mean value for that time period.
我尝试了
df.fillna(df.groupby('period_id','gic_subindustry_id').transform('mean')), 但这似乎太慢了(几分钟后我停了下来).
df.fillna(df.groupby('period_id', 'gic_subindustry_id').transform('mean')), but this seemed to be painfully slow (I stopped it after several minutes).
在我看来,之所以变慢的原因是由于重新计算了遇到的每个NaN的平均值.为了解决这个问题,我认为计算每个period_id的平均值,然后使用此值替换/映射每个NaN可能会更快.
It occurred to me that the reason it might be slow was due to re-calculating the mean for every NaN encountered. To get around this, I thought that calculating the mean at each period_id, and then replacing/mapping each NaN using this might be substantially faster.
means = df.groupby(['period_id', 'gic_subindustry_id']).apply(lambda x:x.mean())
输出:
operating_mgn_fym5 operating_mgn_fym4 operating_mgn_fym3 operating_mgn_fym2
period_id gic_subindustry_id
201509 45202030 1.622685 0.754661 0.755324 321.295665
45203010 1.447686 0.226571 0.334280 12.564398
45203015 0.733524 0.257581 0.345450 27.659407
45203020 1.322349 0.655481 0.468740 19.823722
45203030 1.461916 1.181407 1.487330 16.598534
45301010 2.074954 0.981030 0.841125 29.423161
45301020 2.621158 1.235087 1.550252 82.717147
确实,这要快得多(30-60秒).
And indeed, this is much faster (30 - 60 seconds).
但是,我正在努力弄清楚如何将NaN映射到这些方法.确实,这是执行此映射的正确"方法吗?速度实际上并不是最重要的,但< 60秒会很好.
However, I am struggling to figure out how to map the NaNs to these means. And, indeed, is this the 'correct' way of performing this mapping? Speed actually isn't of paramount importance, but < 60 seconds would be nice.
推荐答案
如果数据框具有相同的结构(由as_index=False
赋予),则可以使用group-by的结果使用fillna
:
You can use fillna
using the result of group-by, provided the dataframes have the same structure (given by as_index=False
):
df.fillna(df.groupby(['period_id', 'gic_subindustry_id'], as_index=False).mean())
#In [60]: df
#Out[60]:
# period_id gic_subindustry_id operating_mgn_fym5 operating_mgn_fym4
#0 201508 25502020 27.688324 22.969760
#1 201508 45102020 17.956425 18.327724
#2 201508 45202020 NaN 27.145216
#3 201509 20101010 10.228725 14.087442
#4 201509 25101010 13.348150 11.745965
#5 201509 25502020 15.598956 11.658813
#6 201509 50101010 27.858305 28.378040
#7 201508 45102020 17.956425 18.327724
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