R对象识别 [英] R object identification

问题描述

我经常得到一个生成输出的函数，但我不了解其输出数据类型.我期待一个列表，它最终成为一个列表列表或一个数据框或其他东西.首次使用函数时确定输出数据类型的好方法或工作流程是什么?

I am often ending up with a function producing output for which I don't understand the output data type. I'm expecting a list and it ends up being a list of lists or a data frame or something else. What's a good method or workflow for figuring out the output data type when first using a function?

推荐答案

我通常从以下组合开始:

I usually start out with some combination of:

typeof(obj)
class(obj)
sapply(obj, class)
sapply(obj, attributes)
attributes(obj)
names(obj)

根据所披露的内容酌情决定.例如，尝试:

as appropriate based on what's revealed. For example, try with:

obj <- data.frame(a=1:26, b=letters)
obj <- list(a=1:26, b=letters, c=list(d=1:26, e=letters))
data(cars)
obj <- lm(dist ~ speed, data=cars)

..等

如果obj是S3或S4对象，你也可以试试methods或showMethods，showClass，等等.Patrick Burns 的 R Inferno 对此有一个很好的部分(第 7 秒).

If obj is an S3 or S4 object, you can also try methods or showMethods, showClass, etc. Patrick Burns' R Inferno has a pretty good section on this (sec #7).

编辑:Dirk 和 Hadley 在他们的回答中提到了 str(obj).对于快速甚至详细地查看对象，它确实比上述任何一种都要好得多.

EDIT: Dirk and Hadley mention str(obj) in their answers. It really is much better than any of the above for a quick and even detailed peek into an object.

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