我有2个数据框,df1
和df2
,并要执行以下操作,将结果存储在中df3
:
for each row in df1:
for each row in df2:
create a new row in df3 (called "df1-1, df2-1" or whatever) to store results
for each cell(column) in df1:
for the cell in df2 whose column name is the same as for the cell in df1:
compare the cells (using some comparing function func(a,b) ) and,
depending on the result of the comparison, write result into the
appropriate column of the "df1-1, df2-1" row of df3)
例如,类似:
df1
A B C D
foo bar foobar 7
gee whiz herp 10
df2
A B C D
zoo car foobar 8
df3
df1-df2 A B C D
foo-zoo func(foo,zoo) func(bar,car) func(foobar,foobar) func(7,8)
gee-zoo func(gee,zoo) func(whiz,car) func(herp,foobar) func(10,8)
我从这里开始:
for r1 in df1.iterrows():
for r2 in df2.iterrows():
for c1 in r1:
for c2 in r2:
但不确定该如何处理,将不胜感激。
因此,要继续在评论中进行讨论,可以使用矢量化,它是pandas或numpy之类的图书馆的卖点之一。理想情况下,您永远不应该打电话iterrows()
。我的建议要更明确一点:
# with df1 and df2 provided as above, an example
df3 = df1['A'] * 3 + df2['A']
# recall that df2 only has the one row so pandas will broadcast a NaN there
df3
0 foofoofoozoo
1 NaN
Name: A, dtype: object
# more generally
# we know that df1 and df2 share column names, so we can initialize df3 with those names
df3 = pd.DataFrame(columns=df1.columns)
for colName in df1:
df3[colName] = func(df1[colName], df2[colName])
现在,您甚至可以通过创建lambda函数,然后使用列名称压缩它们,将不同的函数应用于不同的列:
# some example functions
colAFunc = lambda x, y: x + y
colBFunc = lambda x, y; x - y
....
columnFunctions = [colAFunc, colBFunc, ...]
# initialize df3 as above
df3 = pd.DataFrame(columns=df1.columns)
for func, colName in zip(columnFunctions, df1.columns):
df3[colName] = func(df1[colName], df2[colName])
想到的唯一“陷阱”是,您需要确保您的函数适用于列中的数据。例如,如果您要执行类似的操作df1['A'] - df2['A']
(使用提供的df1,df2),则将产生a,ValueError
因为未定义两个字符串的减法。只是要注意的事情。
编辑,重新:您的评论:这也是可行的。遍历更大的dfX.columns,因此您不会碰到KeyError
,并if
在其中抛出一条语句:
# all the other jazz
# let's say df1 is [['A', 'B', 'C']] and df2 is [['A', 'B', 'C', 'D']]
# so iterate over df2 columns
for colName in df2:
if colName not in df1:
df3[colName] = np.nan # be sure to import numpy as np
else:
df3[colName] = func(df1[colName], df2[colName])
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