如何将列表中的随机值分配给pandas数据框中的列? [英] How to assign random values from a list to a column in a pandas dataframe?
问题描述
我正在Bigquery中使用Python,并且具有较大的数据框df(大约7m行).我还有一个列表lst,其中包含一些日期(例如,给定月份中的所有天).
I am working with Python in Bigquery and have a large dataframe df (circa 7m rows). I also have a list lst that holds some dates (say all days in a given month).
我正在尝试在df中创建一个附加列"random_day",并在每行中使用lst中的随机值.
I am trying to create an additional column "random_day" in df with a random value from lst in each row.
我尝试运行循环并应用函数,但由于数据集很大,因此极富挑战性.
I tried running a loop and apply function but being quite a large dataset it is proving challenging.
我的尝试通过了循环解决方案:
My attempts passed by the loop solution:
df["rand_day"] = ""
for i in a["row_nr"]:
rand_day = sample(day_list,1)[0]
df.loc[i,"rand_day"] = rand_day
然后是应用解决方案,首先定义我的函数,然后调用它:
And the apply solution, defining first my function and then calling it:
def random_day():
rand_day = sample(day_list,1)[0]
return day
df["rand_day"] = df.apply(lambda row: random_day())
对此有任何提示吗? 谢谢
Any tips on this? Thank you
推荐答案
使用 numpy.random.choice
,并在必要时通过 to_datetime
:
df = pd.DataFrame({
'A':list('abcdef'),
'B':[4,5,4,5,5,4],
})
day_list = pd.to_datetime(['2015-01-02','2016-05-05','2015-08-09'])
#alternative
#day_list = pd.DatetimeIndex(['2015-01-02','2016-05-05','2015-08-09'])
df["rand_day"] = np.random.choice(day_list, size=len(df))
print (df)
A B rand_day
0 a 4 2016-05-05
1 b 5 2016-05-05
2 c 4 2015-08-09
3 d 5 2015-01-02
4 e 5 2015-08-09
5 f 4 2015-08-09
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