问题描述
aggregate
的文档指出:
我是R的新手,我不知道这是什么手段。请解释!
I am new to R, and I don't understand what this means. Please explain!
谢谢!
Uri
推荐答案
跳到 help(aggregate)
的示例部分的中间,您将看到:
Jump to the middle of the examples section of help(aggregate)
and you will see this:
## Formulas, one ~ one, one ~ many, many ~ one, and many ~ many:
aggregate(weight ~ feed, data = chickwts, mean)
aggregate(breaks ~ wool + tension, data = warpbreaks, mean)
aggregate(cbind(Ozone, Temp) ~ Month, data = airquality, mean)
aggregate(cbind(ncases, ncontrols) ~ alcgp + tobgp, data = esoph, sum)
对 aggregate()
,全部使用 formula 接口。上面的引用方式与整个R中使用的方法分派机制有关。
Four different calls to aggregate()
, all using the formula interface. The way it is written above in what you quote has to do with method dispatching mechanism used throughout R.
考虑第一个示例:
R> class(weight ~ feed)
[1] "formula"
R> class(chickwts)
[1] "data.frame"
因此总调度第一个参数(属于类公式
)。公式在R中解析的方式通常围绕 model.matrix
,我想这里也会发生类似的情况,并且等效的调用最终会由 aggregate执行.data.frame
,使用第二个参数 chickwts
,一个 data.frame
。
so aggregate dispatches on it first argument (of class formula
). The way a formula gets resolved in R typically revolves around a model.matrix
, I presume something similar happens here and an equivalent call is eventually execucted by aggregate.data.frame
, using the second argument chickwts
, a data.frame
.
R> aggregate(weight ~ feed, data = chickwts, mean)
feed weight
1 casein 323.583
2 horsebean 160.200
3 linseed 218.750
4 meatmeal 276.909
5 soybean 246.429
6 sunflower 328.917
R>
您问的不是最简单的初学者问题,我建议您仔细看一看文档和一本不错的R书(如果有的话)。 (以及其他有关SO的问题为您推荐了下一步的读物。)
What you asked isn't the easiest beginner question, I'd recommend a good thorough look at some of the documentation and a decent R book if you have one handy. (And other SO questions give recommendation as to what to read next.)
编辑:我只得挖掘 aggregate.formula()
不是从 stats
命名空间导出的,但是您可以通过键入 stats来查看它: :: aggregate.formula
在提示符下显示-实际上,它确实分派给 aggregate.data.frame()
:
I had to dig a little as aggregate.formula()
is not exported from stats
namespace, but you can look at it by typing stats:::aggregate.formula
at the prompt -- which then clearly shows that it does, in fact, dispatch to aggregate.data.frame()
:
[.... some code omitted ...]
if (is.matrix(mf[[1L]])) {
lhs <- as.data.frame(mf[[1L]])
names(lhs) <- as.character(m[[2L]][[2L]])[-1L]
aggregate.data.frame(lhs, mf[-1L], FUN = FUN, ...)
}
else aggregate.data.frame(mf[1L], mf[-1L], FUN = FUN, ...)
}
<environment: namespace:stats>
R>
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