背景
前段时间在知识星球上立了一个Flag，至少写10篇关于 Python，Matlab 和 C# 对比的总结。这是第 1 篇，从创建结构、添加元素、删除元素、获取元素四个角度来对比 Matlab 的向量与 Python 的列表。
1. 向量/列表 的创建
1.1 直接法
Matlab
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> disp(x);
"Monday" "Tuesday" "Wednesday" "Thursday" "Friday"
>> whos x
Name Size Bytes Class Attributes
x 1x5 398 string
>> x = [2, 3, 4, 5, 6, 7];
>> disp(x);
2 3 4 5 6 7
>> whos x
Name Size Bytes Class Attributes
x 1x6 48 double
Python
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(x, type(x))
# ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'] <class 'list'>
x = [2, 3, 4, 5, 6, 7]
print(x, type(x))
# [2, 3, 4, 5, 6, 7] <class 'list'>
注：Matlab与Python直接创建向量/列表的方法是相同的，用[ ]括起来，元素用,分割。当然，Matlab中元素也可以用空格来分割。
1.2 等差数列法 – : VS range()
Matlab
>> x = 0:9;
>> disp(x)
0 1 2 3 4 5 6 7 8 9
>> x = 1:2:9;
>> disp(x)
1 3 5 7 9
>> x = 10:-2:1;
>> disp(x)
10 8 6 4 2
Python
x = list(range(10))
print(x, type(x))
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] <class 'list'>
x = list(range(1, 11, 2))
print(x, type(x))
# [1, 3, 5, 7, 9] <class 'list'>
x = list(range(10, 1, -2))
print(x, type(x))
# [10, 8, 6, 4, 2] <class 'list'>
注：Matlab通过:构造的等差数列 左右 都是闭区间，而Python通过range()构造的等差数列是 左闭右开区间。
2. 向量/列表 的元素添加
Matlab
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> x = [x,"Thursday"];
>> disp(x)
"Monday" "Tuesday" "Wednesday" "Thursday" "Friday" "Thursday"
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> x(end+1) = "Thursday";
>> disp(x)
"Monday" "Tuesday" "Wednesday" "Thursday" "Friday" "Thursday"
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> x = [x, ["Thursday","Sunday"]];
>> disp(x)
"Monday" "Tuesday" "Wednesday" "Thursday" "Friday" "Thursday" "Sunday"
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> x = [x(1:2),"Sunday",x(3:end)];
>> disp(x)
"Monday" "Tuesday" "Sunday" "Wednesday" "Thursday" "Friday"
>> x = [123, 456];
>> y = [456, 123];
>> z = [x, y];
>> disp(z)
123 456 456 123
Python
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
x.append('Thursday')
print(x)
# ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Thursday']
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
x.extend(['Thursday', 'Sunday'])
print(x)
# ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Thursday', 'Sunday']
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
x.insert(2, 'Sunday')
print(x)
# ['Monday', 'Tuesday', 'Sunday', 'Wednesday', 'Thursday', 'Friday']
x = [123, 456]
y = [456, 123]
z = x + y # extend()
print(z)
# [123, 456, 456, 123]
注：Matlab的添加元素直接在数组中进行，而Python添加元素是通过append()、extend()、insert()和运算符+来完成。
3. 向量/列表 的元素删除
Matlab
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> x(x == "Monday") = [];
>> disp(x)
"Tuesday" "Wednesday" "Thursday" "Friday"
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> x(end) = [];
>> disp(x)
"Monday" "Tuesday" "Wednesday" "Thursday"
>> x(1) = [];
>> disp(x)
"Tuesday" "Wednesday" "Thursday"
>> x(end -1) = [];
>> disp(x)
"Tuesday" "Thursday"
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> x([1,2]) = [];
>> disp(x)
"Wednesday" "Thursday" "Friday"
Python
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
x.remove('Monday')
print(x) # ['Tuesday', 'Wednesday', 'Thursday', 'Friday']
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
y = x.pop()
print(y) # Friday
y = x.pop(0)
print(y) # Monday
y = x.pop(-2)
print(y) # Wednesday
print(x) # ['Tuesday', 'Thursday']
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
del x[0:2]
print(x) # ['Wednesday', 'Thursday', 'Friday']
注：Matlab通过赋值空数组的方式来删除元素，Python通过remove、pop和内置方法del来删除元素。
4. 向量/列表 的元素获取
Matlab
>> x = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
>> disp(x(1)+" "+class(x(1)))
Monday string
>> disp(x(end)+" "+class(x(end)))
Friday string
>> disp(x(end - 1)+" "+class(x(end - 1)))
Thursday string
>> disp(x(1:3))
"Monday" "Tuesday" "Wednesday"
>> disp(x(1:end - 3))
"Monday" "Tuesday"
>> disp(x(2:2:end))
"Tuesday" "Thursday"
>> disp(x(1:2:end))
"Monday" "Wednesday" "Friday"
>> disp(x(end:-1:1))
"Friday" "Thursday" "Wednesday" "Tuesday" "Monday"
Python
- 通过元素的索引值，从列表获取单个元素，注意，列表索引值是从0开始的。
- 通过将索引指定为-1，可让Python返回最后一个列表元素，索引 -2 返回倒数第二个列表元素，以此类推。
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(x[0], type(x[0])) # Monday <class 'str'>
print(x[-1], type(x[-1])) # Friday <class 'str'>
print(x[-2], type(x[-2])) # Thursday <class 'str'>
切片的通用写法是 start : stop : step
- 情况 1 - “start :”
- 以
step为 1 (默认) 从编号start往列表尾部切片。
x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(x[3:]) # ['Thursday', 'Friday']
print(x[-3:]) # ['Wednesday', 'Thursday', 'Friday']
- 情况 2 - “: stop”
- 以
step为 1 (默认) 从列表头部往编号stop切片。
week = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(week[:3]) # ['Monday', 'Tuesday', 'Wednesday']
print(week[:-3]) # ['Monday', 'Tuesday']
- 情况 3 - “start : stop”
- 以
step为 1 (默认) 从编号start往编号stop切片。
week = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(week[1:3]) # ['Tuesday', 'Wednesday']
print(week[-3:-1]) # ['Wednesday', 'Thursday']
- 情况 4 - “start : stop : step”
- 以具体的
step从编号start往编号stop切片。注意最后把step设为 -1，相当于将列表反向排列。
week = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(week[1:4:2])
# ['Tuesday', 'Thursday']
print(week[:4:2])
# ['Monday', 'Wednesday']
print(week[1::2])
# ['Tuesday', 'Thursday']
print(week[::-1])
# ['Friday', 'Thursday', 'Wednesday', 'Tuesday', 'Monday']
注：Matlab的:对应于Python的切片，只不过Matlab为 start:step:stop而Python为start:stop:step。Python相对于Matlab初始了默认值start=0，stop=len，step=1。
总结
以上总结的不一定全，但先有个框架等后面在实践的过程中慢慢补充。今天就到这里吧。See You！
当前活动
我是 终身学习者“老马”，一个长期践行“结伴式学习”理念的 中年大叔。
我崇尚分享，渴望成长，于2010年创立了“LSGO软件技术团队”，并加入了国内著名的开源组织“Datawhale”，也是“Dre@mtech”、“智能机器人研究中心”和“大数据与哲学社会科学实验室”的一员。
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