从m大小的列索引向量创建0和1的m x n矩阵 [英] Creating an m by n matrix of 0s and 1s from m-sized vector of column indexes

问题描述

我有一个 m 维向量，整数从1到 n .这些整数是 m×n 矩阵的列索引.

I have a m-dimensional vector of integers ranging from 1 to n. These integers are column indexes for m × n matrix.

我想创建一个0s和1s的 m×n 矩阵，其中在 m 行中，由指定的列中有一个1我向量中的第m 个值.

I want to create a m × n matrix of 0s and 1s, where in m-th row there's a 1 in the column that is specified by m-th value in my vector.

示例:

% my vector (3-dimensional, values from 1 to 4):
v = [4;
     1;
     2];

% corresponding 3 × 4 matrix
M = [0 0 0 1;
     1 0 0 0;
     0 1 0 0];

在没有for循环的情况下有可能吗?

Is this possible without a for-loop?

推荐答案

当然，这就是他们发明稀疏矩阵:

Of course, that's why they invented sparse matrices:

>> M = sparse(1:length(v),v,ones(length(v),1))
M =

   (2,1)        1
   (3,2)        1
   (1,4)        1

，如果需要，可以将其转换为完整矩阵，其中完整:

which you can convert to a full matrix if you want with full:

>> full(M)
ans =

     0     0     0     1
     1     0     0     0
     0     1     0     0

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