使用r中的数据框替换列名称

Question

我有矩阵

m <- matrix(1:9, nrow = 3, ncol = 3, byrow = TRUE,dimnames = list(c("s1", "s2", "s3"),c("tom", "dick","bob")))

   tom dick bob
s1   1    2   3
s2   4    5   6
s3   7    8   9

#and the data frame

current<-c("tom", "dick","harry","bob")
replacement<-c("x","y","z","b")
df<-data.frame(current,replacement)

  current replacement
1     tom           x
2    dick           y
3   harry           z
4     bob           b

#I need to replace the existing names i.e. df$current with df$replacement if 
#colnames(m) are equal to df$current thereby producing the following matrix


m <- matrix(1:9, nrow = 3, ncol = 3, byrow = TRUE,dimnames = list(c("s1", "s2", "s3"),c("x", "y","b")))

   x y b
s1 1 2 3
s2 4 5 6
s3 7 8 9

有什么建议？我应该使用'if'循环吗？谢谢.

Answer 1

您可以使用which以匹配colnamesfrom m中的值df$current.然后,当您拥有索引时,可以对替换的列进行子集化df$replacement.

colnames(m) = df$replacement[which(df$current %in% colnames(m))]

在上面:

1. %in%测试TRUE或FALSE比较被比较对象之间的任何匹配.
2. which(df$current %in% colnames(m)) 标识匹配名称的索引(在本例中为行号).
3. df$replacement[...]是列的子集的基本方法,df$replacement只返回与步骤2匹配的行.

Answer 2

查找索引的更直接的方法是使用match:

> id <- match(colnames(m), df$current)
> id
[1] 1 2 4
> colnames(m) <- df$replacement[id]
> m
   x y b
s1 1 2 3
s2 4 5 6
s3 7 8 9

如下所述%in%,通常使用起来更直观,并且效率差异是微不足道的,除非这些集合相对较大,例如

> n <- 50000 # size of full vector
> m <- 10000 # size of subset
> query <- paste("A", sort(sample(1:n, m)))
> names <- paste("A", 1:n)
> all.equal(which(names %in% query), match(query, names))
[1] TRUE
> library(rbenchmark)
> benchmark(which(names %in% query))
                     test replications elapsed relative user.self sys.self user.child sys.child
1 which(names %in% query)          100   0.267        1     0.268        0          0         0
> benchmark(match(query, names))
                 test replications elapsed relative user.self sys.self user.child sys.child
1 match(query, names)          100   0.172        1     0.172        0          0         0