从没有循环的两个数组元素成对创建数组

Question

这里是一个简单的问题。我有数组：

a = [ 600 746 8556 90456 ]
b = [ 684 864 8600 90500 ]

我想得到：

output = [ a(1):b(1) a(2):b(2) a(3):b(3) a(4):b(4) ]

（或者 [ a(1):b(1); a(2):b(2); a(3):b(3); a(4):b(4) ]，我不在乎）

如果不使用循环，我不知道如何做到这一点，但我知道这应该是一种方式。

有什么想法吗？

提前致谢

Answer 1

方法 #1

Vectorized 方法与 bsxfun 的屏蔽能力 -

%// Get "extents" formed with each pair of "a" and "b" and max extent
ext = b-a
max_ext = max(ext)

%// Extend all a's to max possible extent
allvals = bsxfun(@plus,a,[0:max_ext]')  %//'

%// Get mask of valid extensions and use it to have the final output
mask  = bsxfun(@le,[0:max_ext]',ext)  %//'
out  = allvals(mask).'

方法 #2

这里列出的是 cumsum based approach that has to be more memory efficient and faster than both the earlier listed bsxfun based approach and 。这是代码 -

%// Get "extents" formed with each pair of "a" and "b"
ext = b-a;

%// Ignore cases when "a" might be greater than "b"
a = a(ext>=0);
b = b(ext>=0);
ext = b-a;

if numel(ext)>1

    %// Strategically place "differentiated" values from array,a
    idx = ones(sum(ext+1),1);
    idx([1 cumsum(ext(1:end-1)+1)+1]) = [a(1) diff(a)-ext(1:end-1)];

    %// Perform cumulative summation to have the final output
    out = cumsum(idx)

else %// Leftover cases when there are one or no valid boundaries:(a->b)
    out = a:b
end

样本运行-

>> a
a =
     6    12    43
>> b
b =
     8    17    43
>> out
out =
     6     7     8    12    13    14    15    16    17    43

Answer 2

单行使用 arrayfun, cell2mat and an anonymous function:

output = cell2mat(arrayfun(@(start, stop) start:stop, a, b, 'uni', 0))

解释：函数 arrayfun 并行迭代向量 a 和 b，然后为它们的每一对元素调用匿名函数。匿名函数return是一个变长向量而不是标量，所以需要用'UniformOutput', false（可以简写为'uni', 0）使arrayfunreturn 元胞数组。最后，您使用 cell2mat 将元胞数组一起压缩成一个向量。

快速测试：

>> a = [10, 20, 40];
>> b = [13, 22, 45];
>> output = cell2mat(arrayfun(@(start, stop) start:stop, a, b, 'uni', 0))
output =
    10    11    12    13    20    21    22    40    41    42    43    44    45

从没有循环的两个数组元素成对创建数组

Create array from two arrays elements in pairs without loops

arrays

matlab

vector

vectorization