select first occurrence where column value is greater than x for each A(key) | dataframe

What I have

   A    B    C  D  E
0  foo  0  1.2  1  2
1  foo  1  1.3  2  4
2  foo  2  2.1  4  5
3  foo  3  3.1  3  5
4  nan  0    0  0  0
5  bar  0  4.1  4  6
6  bar  1  1.2  5  8
7  bar  2  1.4  6  9
8  bar  3  5.0  7  9
9  nan  0    0  0  0
10 baz  0  4.1  5  0
11 baz  1  1.2  5  3
12 baz  2  1.4  6  9
13 baz  3  5.0  7  9

What I want, select first occurrence where D >= 4 for each A(key)

So end result will look like,

   A    B    C  D  E
0  foo  2  2.1  4  5
1  bar  0  4.1  4  6
2  baz  0  4.1  5  0

Answer

You can first slice the rows that match the condition on D, then groupby A and get the first element of each group:

df[df['D'].ge(4)].groupby('A', sort=False).first()

output:

     B    C  D  E
A                
foo  2  2.1  4  5
bar  0  4.1  4  6
baz  0  4.1  5  0