我有一个相当大(约5000行)的数据帧,有许多变量,比如2['max','min',按4个参数排序,['Hs','Tp','wd','seed']。看起来是这样的:
>>> data.head()
Hs Tp wd seed max min
0 1 9 165 22 225 18
1 1 9 195 16 190 18
2 2 5 165 43 193 12
3 2 10 180 15 141 22
4 1 6 180 17 219 18
>>> len(data)
4500
我只想保留前2个参数,并获得每个'wd'单独计算的所有'seed'的最大标准偏差。你知道吗
最后,给我留下了唯一的(Hs,Tp)对,每个变量都有最大的标准差。比如:
>>> stdev.head()
Hs Tp max min
0 1 5 43.31321 4.597629
1 1 6 43.20004 4.640795
2 1 7 47.31507 4.569408
3 1 8 41.75081 4.651762
4 1 9 41.35818 4.285991
>>> len(stdev)
30
下面的代码实现了我想要的功能,但是由于我对DataFrames知之甚少,我想知道这些嵌套循环是否可以用一种不同的、更多的dataframe方式来完成()
import pandas as pd
import numpy as np
#
#data = pd.read_table('data.txt')
#
# don't worry too much about this ugly generator,
# it just emulates the format of my data...
total = 4500
data = pd.DataFrame()
data['Hs'] = np.random.randint(1,4,size=total)
data['Tp'] = np.random.randint(5,15,size=total)
data['wd'] = [[165, 180, 195][np.random.randint(0,3)] for _ in xrange(total)]
data['seed'] = np.random.randint(1,51,size=total)
data['max'] = np.random.randint(100,250,size=total)
data['min'] = np.random.randint(10,25,size=total)
# and here it starts. would the creators of pandas pull their hair out if they see this?
# can this be made better?
stdev = pd.DataFrame(columns = ['Hs', 'Tp', 'max', 'min'])
i=0
for hs in set(data['Hs']):
data_Hs = data[data['Hs'] == hs]
for tp in set(data_Hs['Tp']):
data_tp = data_Hs[data_Hs['Tp'] == tp]
stdev.loc[i] = [
hs,
tp,
max([np.std(data_tp[data_tp['wd']==wd]['max']) for wd in set(data_tp['wd'])]),
max([np.std(data_tp[data_tp['wd']==wd]['min']) for wd in set(data_tp['wd'])])]
i+=1
谢谢!你知道吗
附言:如果好奇的话,这是根据海浪变化的统计数据。Hs是波高、Tp波周期、wd波方向,种子代表一个不规则波列的不同实现,min和max是某一曝光时间内的峰值或my变量。在所有这些之后,通过标准差和平均值,我可以对数据拟合一些分布,比如Gumbel。你知道吗
如果我理解正确的话,这可能是一行:
(如果您愿意,可以在末尾加上
reset_index()
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