[英]How to apply several functions to a single pandas dataframe column?
[英]How to apply multiple functions onto a single DataFrame column?
說我有df:
Name Sequence
Bob IN,IN
Marley OUT,IN
Jack IN,IN,OUT,IN
Harlow
df 具有名稱和“輸入/輸出”序列。 序列列中可以有空白值。 如何以有效的方式將這兩個函數應用於序列列? 像這樣的偽代碼:
df['Sequence'] = 轉換器(sequencer(df['Sequence']))
# takes string of IN/OUT, converts to bits, returns bitstring. 'IN,OUT,IN' -> '010'
def sequencer(seq):
# 'IN,IN' -> ['IN', 'IN']
seq = seq.split(',')
# get sequence up to 3 unique digits. [0,0,1,1,0] = sequence 010
seq = [1 if x == 'IN' else 0 for x in seq]
a = seq[0]
try:
b = seq.index(1-a, 1)
except:
return str(a)
if a not in seq[b+1]:
return str(a) + str(1-a)
return str(a) + str(1-a) + str(a)
# converts bitstring back into in/out format
def converter(seq):
return '-'.join(['IN' if x == '1' else 'OUT' for x in seq])
導致這個 dataframe?
Name Sequence
Bob IN
Marley OUT-IN
Jack IN-OUT-IN
Harlow
我在這里看了這篇文章,評論說不要使用 apply,因為它效率低下,我需要效率,因為我正在處理一個大型數據集。
itertools
groupby
獲得獨特(不重復)的東西islicde
獲得前 3 個。from itertools import islice, groupby
def f(s):
return '-'.join([k for k, _ in islice(groupby(s.split(',')), 3)])
df.assign(Sequence=[*map(f, df.Sequence.fillna(''))])
Name Sequence
0 Bob IN
1 Marley OUT-IN
2 Jack IN-OUT-IN
3 Harlow
具有更好封閉性的變體,可實現最大的未來靈活性。
from itertools import islice, groupby
def get_f(n, splitter=',', joiner='-'):
def f(s):
return joiner.join([k for k, _ in islice(groupby(s.split(splitter)), n)])
return f
df.assign(Sequence=[*map(get_f(3), df.Sequence.fillna(''))])
另一個讓我在做什么更明顯的變體(不那么令人討厭的 Python bling)
from itertools import islice, groupby
def get_f(n, splitter=',', joiner='-'):
def f(s):
return joiner.join([k for k, _ in islice(groupby(s.split(splitter)), n)])
return f
f = get_f(3)
df['Sequence-InOut'] = [f(s) for s in df.Sequence.fillna('')]
df
Name Sequence Sequence-InOut
0 Bob IN,IN IN
1 Marley OUT,IN OUT-IN
2 Jack IN,IN,OUT,IN IN-OUT-IN
3 Harlow None
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