tapply和ave之间的功能有什么区别？ [英] What is the difference between the functions tapply and ave?

问题描述

我不能全神贯注于 ave 函数。我阅读了帮助并搜索了网络，但仍然无法理解它的作用。我了解它在观察的子集上应用了某些功能，但不是像 tapply

I can't wrap my mind around the ave function. I read the help and searched the net but I still cannot understand what it does. I understand it applies some function on a subset of observation but not in the same way as for example tapply

有人请举个小例子来启发我吗？

Could someone please enlighten me perhaps with a small example?

谢谢，请原谅我一个不寻常的请求。

Thanks, and excuse me for perhaps an unusual request.

推荐答案

tapply 返回每个因子水平的单个结果。 ave 还会在每个因子水平上产生单个结果，但会将其复制到原始数据中的每个位置。

tapply returns a single result for each factor level. ave also produces a single result per factor level, but it copies this value to each position in the original data.

ave 在包含摘要数据的数据框中生成新列非常方便。

ave is handy for producing a new column in a data frame with summary data.

一个简短的示例：

tapply(iris$Sepal.Length, iris$Species, FUN=mean)
    setosa versicolor  virginica 
     5.006      5.936      6.588 

一个值，每个因子水平的平均值。

One value, the mean for each factor level.

ave 产生150个结果，该结果与原始数据框一致：

ave on iris produces 150 results, which line up with the original data frame:

 ave(iris$Sepal.Length, iris$Species, FUN=mean)
  [1] 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006
 [17] 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006
 [33] 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006
 [49] 5.006 5.006 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936
 [65] 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936
 [81] 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936
 [97] 5.936 5.936 5.936 5.936 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588
[113] 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588
[129] 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588
[145] 6.588 6.588 6.588 6.588 6.588 6.588

如评论中所述，此处将回收单个值以填充每个值

As noted in the comments, here the single value is being recycled to fill each location in the original data.

如果函数返回多个值，则如有必要，将回收这些值以填充位置。例如：

If the function returns multiple values, these are recycled if necessary to fill in the locations. For example:

d <- data.frame(a=rep(1:2, each=5), b=1:10)
ave(d$b, d$a, FUN=rev)
 [1]  5  4  3  2  1 10  9  8  7  6

感谢Josh和thelatemail。

Thanks to Josh and thelatemail.

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