python - 按值在总计行中的百分比替换值

Question

用连续的百分比替换某些列中的值的最直接方法是什么？

示例:

由此

对此

我试过代码:

cols=['h1', 'h2', 'h3', 'hn']
df[cols]=df[cols]/df['sum']

但这会返回错误:

ValueError: Columns must be same length as key.

此外，我认为这不是最好的方法，因为我的列数可能比 4 列多得多。

Answer 1

使用DataFrame.div指定 axis=0:

cols=['h1', 'h2', 'h3', 'hn']
df[cols]=df[cols].div(df['sum'], axis=0)

如果 sum 是最后一列，则可以使用:

df.iloc[:, :-1]=df.iloc[:, :-1].div(df['sum'], axis=0)

示例:

df = pd.DataFrame({
         'h1':[4,5,4,5,5,4],
         'h2':[7,8,9,4,2,3],
         'h3':[1,3,5,7,1,0],
         'hn':[4,5,4,5,5,4],
})
df['sum'] = df.sum(axis=1)

df.iloc[:, :-1] = df.iloc[:, :-1].div(df['sum'], axis=0)
print (df)
         h1        h2        h3        hn  sum
0  0.250000  0.437500  0.062500  0.250000   16
1  0.238095  0.380952  0.142857  0.238095   21
2  0.181818  0.409091  0.227273  0.181818   22
3  0.238095  0.190476  0.333333  0.238095   21
4  0.384615  0.153846  0.076923  0.384615   13
5  0.363636  0.272727  0.000000  0.363636   11

性能:

np.random.seed(2019)

N = 10000
df = pd.DataFrame(np.random.randint(100, size=(N, 20))).add_prefix('h')
df['sum'] = df.sum(axis=1)
print (df)

In [220]: %%timeit
     ...: df.iloc[:, :-1]=df.iloc[:, :-1].div(df['sum'], axis=0)
     ...: 
8.03 ms ± 1.05 ms per loop (mean ± std. dev. of 7 runs, 100 loops each)
C:\Anaconda\lib\site-packages\spyder\widgets\variableexplorer\utils.py:410: FutureWarning: 'summary' is deprecated and will be removed in a future version.
  display = value.summary()

In [221]: %%timeit
     ...: for col in df.columns[:-1]:
     ...:     df[col] /= df["sum"]
     ...: 
9.46 ms ± 168 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
C:\Anaconda\lib\site-packages\spyder\widgets\variableexplorer\utils.py:410: FutureWarning: 'summary' is deprecated and will be removed in a future version.
  display = value.summary()

In [222]: %%timeit
     ...: df.iloc[:,:-1] = df.iloc[:,:-1].apply(lambda x: x/sum(x), axis=1)
     ...: 
2.51 s ± 194 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
C:\Anaconda\lib\site-packages\spyder\widgets\variableexplorer\utils.py:410: FutureWarning: 'summary' is deprecated and will be removed in a future version.
  display = value.summary()