二维数组转置

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var arr=[['a','b','c'],['d','e','f'],['g','h','i'],['j','k','l']];             var res=[];             for(var i=0;i<arr[0].length;i++){                 res[i]=[];                 for(var j=0;j<arr.length;j++){                     res[i][j]=arr[j][i];                 }             }             console.group('转置前：');             console.log(arr);             console.groupEnd();             console.group('转置后：');             console.log(res);             console.groupEnd();