我们分别对sep，collapse，step三个元素进行试验
> paste(1:10,sep=",")
[1] "1"  "2"  "3"  "4"  "5"  "6"  "7"  "8"  "9"  "10"
> paste(1:10,1,sep=",")
[1] "1,1"  "2,1"  "3,1"  "4,1"  "5,1"  "6,1"  "7,1"  "8,1"  "9,1"  "10,1"
> paste(1:10,collapse=",")
[1] "1,2,3,4,5,6,7,8,9,10"
> paste(1:10,1,collapse=",")
[1] "1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 1,10 1"
> paste(1:10,step=",")
[1] "1 ,"  "2 ,"  "3 ,"  "4 ,"  "5 ,"  "6 ,"  "7 ,"  "8 ,"  "9 ,"  "10 ,"
> paste(1:10,1,step=",")
[1] "1 1 ,"  "2 1 ,"  "3 1 ,"  "4 1 ,"  "5 1 ,"  "6 1 ,"  "7 1 ,"  "8 1 ,"  "9 1 ,"  "10 1 ,"
> paste(1:10,1)
[1] "1 1"  "2 1"  "3 1"  "4 1"  "5 1"  "6 1"  "7 1"  "8 1"  "9 1"  "10 1"
在未设定参数的情况下，paste (..., sep = " ", collapse = NULL)，即sep默认是空格，collapse默认为NULL，step也应为NULL
我们定义元素A1和B1为一对组合，则A1B1和A2B2为两对组合，可以判断，对于A,B这两个对象执行paste(A,B)，
sep是对每对组合即A1和B1的分隔
collapse是对组合之间即A1B1和A2B2的分隔
而step是在每对组合后面再添加一个元素
因此可以看到
> paste(rep(1,10),0,sep="a",step="b",collapse="c")
[1] "1a0abc1a0abc1a0abc1a0abc1a0abc1a0abc1a0abc1a0abc1a0abc1a0ab"
为了更直观的认识step，
> paste(1:10,1,sep=",")
[1] "1,1"  "2,1"  "3,1"  "4,1"  "5,1"  "6,1"  "7,1"  "8,1"  "9,1"  "10,1"
> paste(1:10,sep=",",step=1)
[1] "1,1"  "2,1"  "3,1"  "4,1"  "5,1"  "6,1"  "7,1"  "8,1"  "9,1"  "10,1"
可以看到，这两个结果是一样的

谢谢，非常感谢，学习了

多试几个例子，其实就能看出差别了，没什么悬乎的哈