Comprehensions
給 R 使用者的 Python
Daniel Chen
Instructor
Comprehensions 就是迴圈
- 迭代（loop）串列
- 執行函式
- 將結果加入新串列
List comprehension
迴圈
data = [1, 2, 3, 4, 5]
new = []
for x in data:
new.append(x**2)
print(new)
[1, 4, 9, 16, 25]
Comprehension
data = [1, 2, 3, 4, 5]
new = [x**2 for x in data]
print(new)
[1, 4, 9, 16, 25]
Dictionary comprehension
迴圈
data = [1, 2, 3, 4, 5]
new = {}
for x in data:
new[x] = x**2
print(new)
{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
Comprehension
data = [1, 2, 3, 4, 5]
new = {x: x**2 for x in data}
print(new)
{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
取代 `for` 迴圈的作法
- 用
for迴圈來走訪 - R：
sapply、lapply、apply函式 - Python：
map函式與apply方法
Map
For 迴圈
def sq(x):
return x**2
l = [1, 2, 3]
for i in l:
print(sq(i))
1
4
9
Map
map(sq, l)
<map at 0x7f41cca38358>
list(map(sq, l))
[1, 4, 9]
一起來練習吧！
給 R 使用者的 Python
