如何显示第n行和最后一行

Question

我需要使用pandas显示第n行和最后一行。我知道可以使用iloc

显示第n行

例如：

data = {"x1": [1,2,3,4,5,6,7,8,9,10], "x2": ["a","b","c","d","e","f","g","h","i","j"]}
df = pd.DataFrame(data=data)
a = df.iloc[::2]
print(a)

将显示

   x1 x2
0   1  a
2   3  c
4   5  e
6   7  g
8   9  i

但我需要它：

   x1 x2
0   1  a
2   3  c
4   5  e
6   7  g
8   9  i
9  10  j

如何实现？

Answer 1

使用union个索引，如果默认为loc，则按RangeIndex选择：

a = df.loc[df.index[::2].union([df.index[-1]])]
print(a)
   x1 x2
0   1  a
2   3  c
4   5  e
6   7  g
8   9  i
9  10  j

<强>详细：

print(df.index[::2].union([df.index[-1]]))
Int64Index([0, 2, 4, 6, 8, 9], dtype='int64')

另一种更通用的解决方案：

data = {"x1": [1,2,3,4,5,6,7,8,9,10], "x2": ["a","b","c","d","e","f","g","h","i","j"]}
df = pd.DataFrame(data=data, index=[0]*10)
print (df)
   x1 x2
0   1  a
0   2  b
0   3  c
0   4  d
0   5  e
0   6  f
0   7  g
0   8  h
0   9  i
0  10  j

arr = np.arange(len(df.index))
a = df.iloc[np.union1d(arr[::2], [arr[-1]])]
print(a)
   x1 x2
0   1  a
0   3  c
0   5  e
0   7  g
0   9  i
0  10  j