大熊貓列值合併

Question

我有一個這樣的熊貓數據幀：

df = pd.DataFrame({'a1':['astr1','jmtr2','astr2','mmsk3', 
         'astr6','jmtr2','astr2','mhhk', 
         'astr5','mmsk','astr6','astr1', 
         'mstr1','mhhk','mstr2','mhhk'], 
        'a2':[x for x in np.random.randn(16)]}) 
df 

    a1  a2 
0 astr1 -0.490416 
1 jmtr2 0.651627 
2 astr2 0.784004 
3 mmsk3 -1.595870 
4 astr6 1.228631 
5 jmtr2 -1.644518 
6 astr2 -0.311709 
7 mhhk -1.284221 
8 astr5 -0.356339 
9 mmsk -0.071046 
10 astr6 1.620838 
11 astr1 -0.717384 
12 mstr1 0.830618 
13 mhhk -0.020226 
14 mstr2 -0.056465 
15 mhhk -0.160234 

我想現在要做的是合併a1如果前四個字母是一樣的。同時，應該添加a2的值。

像這樣：

a1  a2 
0 astr $sum of astr$ 
1 jmtr $sum of jmtr$ 
2 mmsk $sum of mmsk$ 
3 mhhk $sum of mhhk$ 
4 mstr $sum of mstr$ 

Answer 1

我認爲你需要的a1第一4字符groupby與indexing with str和骨料sum：

print (df.a1.str[:4]) 
0  astr 
1  jmtr 
2  astr 
3  mmsk 
4  astr 
5  jmtr 
6  astr 
7  mhhk 
8  astr 
9  mmsk 
10 astr 
11 astr 
12 mstr 
13 mhhk 
14 mstr 
15 mhhk 
Name: a1, dtype: object 

print (df.a2.groupby(df.a1.str[:4]).sum().reset_index()) 
    a1  a2 
0 astr 1.112200 
1 jmtr -1.559358 
2 mhhk 1.113222 
3 mmsk -0.023918 
4 mstr -2.526466