在子集函数和逻辑运算符中使用多个条件 [英] Using multiple criteria in subset function and logical operators

问题描述

如果要在R中选择数据的子集，则可以使用子集功能.我想根据符合以下几个条件之一的数据进行分析:某个变量是1、2或3. 我尝试过

If I want to select a subset of data in R, I can use the subset function. I wanted to base an analysis on data that that was matching one of a few criteria, e.g. that a certain variable was either 1, 2 or 3. I tried

myNewDataFrame <- subset(bigfive, subset = (bigfive$bf11==(1||2||3)))

它总是只选择与第一个条件匹配的值，这里是1.我的假设是，它将以1开头，如果它的计算结果为"false"，则将继续为2，然后为3，然后如果没有匹配项，则==之后的语句为"false"，如果其中之一匹配，则为"true".

It did always just select values that matched the first of the criteria, here 1. My assumption was that it would start with 1 and if it does evaluate to "false" it would go on to 2 and than to 3, and if none matches the statement after == is "false" and if one of them matches, it is "true".

我使用

 newDataFrame <- subset(bigfive, subset = (bigfive$bf11==c(1,2,3)))

但是我希望能够通过逻辑运算符选择数据，所以:为什么第一种方法不起作用?

But I would like to be able to select data via logical operators, so: why did the first approach not work?

推荐答案

此处的正确运算符为%in%.这是虚拟数据的示例:

The correct operator is %in% here. Here is an example with dummy data:

set.seed(1)
dat <- data.frame(bf11 = sample(4, 10, replace = TRUE),
                  foo = runif(10))

给予:

> head(dat)
  bf11       foo
1    2 0.2059746
2    2 0.1765568
3    3 0.6870228
4    4 0.3841037
5    1 0.7698414
6    4 0.4976992

dat的子集(其中bf11等于任何集合1,2,3)是使用%in%进行的:

The subset of dat where bf11 equals any of the set 1,2,3 is taken as follows using %in%:

> subset(dat, subset = bf11 %in% c(1,2,3))
   bf11       foo
1     2 0.2059746
2     2 0.1765568
3     3 0.6870228
5     1 0.7698414
8     3 0.9919061
9     3 0.3800352
10    1 0.7774452

关于您的原件不起作用的原因，请对其进行分解以查看问题.查看1||2||3的计算结果:

As to why your original didn't work, break it down to see the problem. Look at what 1||2||3 evaluates to:

> 1 || 2 || 3
[1] TRUE

，您将使用|获得相同的结果.结果，subset()调用将仅返回bf11为TRUE的行(或计算为TRUE的行).

and you'd get the same using | instead. As a result, the subset() call would only return rows where bf11 was TRUE (or something that evaluated to TRUE).

您本可以写的东西会是这样的:

What you could have written would have been something like:

subset(dat, subset = bf11 == 1 | bf11 == 2 | bf11 == 3)

给出的结果与我先前的subset()调用相同.关键是您需要一系列的单个比较，而不是一系列选项的比较.但是正如您所看到的，在这种情况下，%in%更加有用，而且不那么冗长.还要注意，由于要依次比较bf11和1，2和3的每个元素，因此必须使用|.比较:

Which gives the same result as my earlier subset() call. The point is that you need a series of single comparisons, not a comparison of a series of options. But as you can see, %in% is far more useful and less verbose in such circumstances. Notice also that I have to use | as I want to compare each element of bf11 against 1, 2, and 3, in turn. Compare:

> with(dat, bf11 == 1 || bf11 == 2)
[1] TRUE
> with(dat, bf11 == 1 | bf11 == 2)
 [1]  TRUE  TRUE FALSE FALSE  TRUE FALSE FALSE FALSE FALSE  TRUE

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