请参考R中的名称范围 [英] refer to range of columns by name in R

问题描述

我需要帮助R中可能相当简单的内容。我想参考数据框中的一列列（例如，提取几个选择变量）。但是，我不知道他们的列号。通常，如果我想提取第4-10栏，我会说mydata [，4：10]。

但是，鉴于我不知道列号，我想通过名称引用它们。有没有办法做到这一点？在sas或spss中，通过名称引用一系列变量是相当容易的。或者，有没有一个简单的方法来确定哪个列号对应于R中的变量名？

解决方案

使用％in％与 names（）相结合。从数据框中抓取一组列是有用的。当您想保留一个子集并放弃其余部分时，您可以否定表达式。在R控制台提示下输入？％％in。

  set.seed（1234）
 mydf<  -  data.frame（A = runif（5，1，2），
 B = runif（5，3，4），
 C = runif（5，5，6），
 D = runif（5，7，8），
 E = runif（5，9，10））
 mydf 
 
 keep.cols<  -  c（'A'，'D'，'E'）
 mydf [，name（mydf）％in％keep.cols] 
 drop.cols <  -  c（'A'，'B'，'C'）
 mydf [，！name（mydf）％in％drop.cols] 
  

数据框：

 > mydf 
 ABCDE 
 1 1.113703 3.640311 5.693591 7.837296 9.316612 
 2 1.622299 3.009496 5.544975 7.286223 9.302693 
 3 1.609275 3.232551 5.282734 7.266821 9.159046 
 4 1.623379 3.666084 5.923433 7.186723 9.039996 
 5 1.860915 3.514251 5.292316 7.232226 9.218800 
  

列的一部分：

 > mydf [，名称（mydf）％在％keep.cols] 
 ADE 
 1 1.113703 7.837296 9.316612 
 2 1.622299 7.286223 9.302693 
 3 1.609275 7.266821 9.159046 
 4 1.623379 7.186723 9.039996 
 5 1.860915 7.232226 9.218800 
  

保留列的一部分并删除其余部分： p>

 > mydf [，！name（mydf）％in％drop.cols] 
 DE 
 1 7.837296 9.316612 
 2 7.286223 9.302693 
 3 7.266821 9.159046 
 4 7.186723 9.039996 
 5 7.232226 9.218800 
  

I need help with something that might be fairly simple in R. I want to refer to a range of columns in a data frame (e.g., extracting a few select variables). However, I don't know their column numbers. Normally, if I wanted to extract columns 4-10 i would say mydata[,4:10].

However, given that I don't know the column numbers, I would want to refer to them by name. Is there an easy way to do this? in sas or spss it is fairly easy to refer to a range of variables by name. Alternatively, is there an easy way to figure out which column number corresponds to a variable name in R?

解决方案

Use %in% in combination with names(). It's useful for grabbing a group of columns from a data frame. You can negate the expression when you want to keep just a subset and drop the rest. Type ?"%in%" at the R Console prompt for more details.

set.seed(1234)
mydf <- data.frame(A = runif(5, 1, 2),
                   B = runif(5, 3, 4),
                   C = runif(5, 5, 6),
                   D = runif(5, 7, 8),
                   E = runif(5, 9, 10))
mydf

keep.cols <- c('A','D','E')
mydf[, names(mydf) %in% keep.cols]
drop.cols <- c('A','B','C')
mydf[, !names(mydf) %in% drop.cols]

The data frame:

> mydf
         A        B        C        D        E
1 1.113703 3.640311 5.693591 7.837296 9.316612
2 1.622299 3.009496 5.544975 7.286223 9.302693
3 1.609275 3.232551 5.282734 7.266821 9.159046
4 1.623379 3.666084 5.923433 7.186723 9.039996
5 1.860915 3.514251 5.292316 7.232226 9.218800

A subset of columns:

> mydf[, names(mydf) %in% keep.cols]
         A        D        E
1 1.113703 7.837296 9.316612
2 1.622299 7.286223 9.302693
3 1.609275 7.266821 9.159046
4 1.623379 7.186723 9.039996
5 1.860915 7.232226 9.218800

Keeping a subset of columns and dropping the rest:

> mydf[, !names(mydf) %in% drop.cols]
         D        E
1 7.837296 9.316612
2 7.286223 9.302693
3 7.266821 9.159046
4 7.186723 9.039996
5 7.232226 9.218800

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