同步回调（synchronous callback）是一种编程模式，在这种模式中，回调函数会在调用它的代码中被同步执行。简单来说，就是在调用回调函数的地方等待它完成，然后再继续执行后续的代码。
I am working with a large list of points (each point has three dimensions x,y,z). I am pretty new with R, so I would like to know what is the best way to represent that kind of information.As far as
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