如何使用嵌套循环访问一维数组中的元素？

Question

我需要将以下数据存储在一个向量中（按此顺序）：

cAge[0]  = 'Age (1) (1)';
cAge[1]  = 'Age (1) (2)';
cAge[2]  = 'Age (1) (3)';
cAge[3]  = 'Age (2) (1)';
cAge[4]  = 'Age (2) (2)';
cAge[5]  = 'Age (2) (3)';
cAge[6]  = 'Age (3) (1)';
cAge[7]  = 'Age (3) (2)';
cAge[8]  = 'Age (3) (3)';
cAge[9]  = 'Age (4) (1)';
cAge[10] = 'Age (4) (2)';
cAge[11] = 'Age (4) (3)';

我可以毫无问题地使用for 循环来做到这一点：

var cAge = [];

for (var i=1; i<=4; i++) {
  for (var j=1; j<=3; j++) {
    cAge.push('Age (' + i + ')' + ' ' + '(' + j + ')');
  }
}

但是我无法使用以下嵌套循环显示所有这些：

for (var i=1; i<=4; i++) {
  for (var j=1; j<=3; j++) {
    console.log(cAge[j-1]); // <- What should j-1 be?
  }
}

它产生：

Age (1) (1)
Age (1) (2)
Age (1) (3)
Age (1) (1)
Age (1) (2)
Age (1) (3)
Age (1) (1)
Age (1) (2)
Age (1) (3)
Age (1) (1)
Age (1) (2)
Age (1) (3)

j-1 应该是什么？

Answer 1

使用嵌套循环访问一维数组中的元素：

const cAge = [],
  nrows = 4,
  ncols = 3;

for (var i = 1; i <= nrows; i++) {
  for (var j = 1; j <= ncols; j++) {
    cAge.push("Age (" + i + ")" + " " + "(" + j + ")");
  }
}

for (var i = 0; i < nrows; i++) {
  for (var j = 0; j < ncols; j++) {
    console.log(cAge[i * ncols + j]);
  }
}

这里，ncols = 3

i in nested loop	j in nested loop	1-D index
0	0	0 * 3 + 0 = 0
0	1	0 * 3 + 1 = 1
0	2	0 * 3 + 2 = 2
1	0	1 * 3 + 0 = 3
1	1	1 * 3 + 1 = 4
1	2	1 * 3 + 2 = 5
2	0	2 * 3 + 0 = 6
2	1	2 * 3 + 1 = 7
2	2	2 * 3 + 2 = 8