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[英]Pandas, how to find rows that meet certain conditions and save the previous row in a new dataframe
[英]Pandas Dataframe: Find the conditional mean of all observations that meet certain conditions that are DIFFERENT in each row
假设我有一个像这样的数据框:
date M1_start M1_end SimPrices_t0_exp
0 2017-12-31 2018-01-01 2018-01-31 16.151667
1 2018-01-01 2018-02-01 2018-02-28 45.138445
2 2018-01-02 2018-02-01 2018-02-28 56.442648
3 2018-01-03 2018-02-01 2018-02-28 59.769931
4 2018-01-04 2018-02-01 2018-02-28 50.171695
我想获得SimPrices_t0_exp观测值的平均值,对于每个观测值,其“日期”的值都在M1_start和M1_end之间
我已经试过了
mask = ((df['date'] >= df['M1_start']) & (df['date'] <= df['M1_end']))
df['mymean'] = df['SimPrices_t0_exp'][mask].mean()
我相信每次观察都会返回NaN的原因,我相信是因为对每一行都应用了掩码,因此需要逐一检查掩码条件以获取其自己的日期(永远不会返回true)。
有人可以帮我吗? 我已经为这个问题苦苦挣扎了两天
示例:对于第一个观察,在此特定情况下,结果列在其第一个观察中将具有平均45.13,56.44,59.76,50.17
如果对某人有帮助,则伪代码将如下所示:
for obs in observations:
start = obs.start
end = obs.end
sum = 0
obs_count = 0
for obs2 in observations:
if obs2.date >= start and obs2.date <= end:
sum += obs.SimPrices_t0_exp
obs_count += 1
obs.mean = sum/obs_count
谢谢!!
在这里,一种使用笛卡尔合并(对于大型数据集不是一个好的选择),过滤和groupby
方法来做到这一点:
df = df.assign(key=1)
df_m = df.merge(df, on='key')
df_m.query('M1_start_x <= date_y <= M1_end_x').groupby(['M1_start_x','M1_end_x'])['SimPrices_t0_exp_y'].mean()
输出:
M1_start_x M1_end_x
2018-01-01 2018-01-31 52.88068
Name: SimPrices_t0_exp_y, dtype: float64
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