r-如何在变量中使用变量 [英] r - how to use a variable in a variable

问题描述

我有一个数据框，其中行名是单词，我可以使用

I have a data frame where the row names are words and I can call the first column of that row of data drame using something like

>df['rowB',1]

我知道我可以使用粘贴

>paste("the value is ", df['rowB',1], "."]

，这将使我得到带有如果rowname是一个等于'rowB？的变量，该怎么办？我试图在上面的粘贴中添加第一个粘贴，但是第一个粘贴的结果并没有移到该值上，而是一个

and that will get me an output of the string with the value of the variable. what if rowname is a variable that equals 'rowB? I tried to do a first paste to put in the paste above, but the result of the first paste doesn't evaulate to the value, but rather is just a string that says

>rowname<-'rowB'
>type<-paste("relatype[\'", rowname, "\',1]", sep="")
'df['rowB',1]'

长话短说，我想输入一个名为行名的值作为函数的参数，并对其进行计算以获取rown的值ame，因此我可以将该值放入同一函数中的字符串中。

long story short, I want to input a value called 'rowname' as a parameter of a function and have it be evaluated for the value of rowname, so I can then put that value into a string within that same function.

我也欢迎使用完全不同的解决方案。

I'm also open to a wholly different solution. any and all suggestions are welcome.

谢谢

推荐答案

不确定问题可能是什么，从您的描述中还不能完全清楚，但是如果行名是一个变量，则不需要任何特殊的东西，因为无论如何它都会求值。让

Not sure what the problem might be, not entirely clear from your description, but if rowname is a variable, you don't need anything special, because it will evaluate to it's value anyway. Let

mat <- matrix(1:10, nrow = 5)
rownames(mat) <- letters[1:5]
mat
##   [,1] [,2]
##a    1    6
##b    2    7
##c    3    8
##d    4    9
##e    5   10

rowname<- b ，然后

rowname
##[1] "b"

所以

mat[rowname, 1]
##b 
##2 

与 mat [ b，1] 相同。如果您使用 mat ['rowname'，1] ，它只会失败。
如果要将其放入函数中，则可以执行以下操作：

which is the same as mat["b", 1]. It only fails, if you use mat['rowname', 1]. If you want to put this in functions, you can do something like:

getElement <- function(mat, row.name, column.index) {

    mat[row.name, column.index]

}


getElement(mat, "b", 1)
##b 
##2 

pasteSenstence <- function(mat, row.name, col.index) {

    paste("The element of row", row.name, "and column", col.index, "is", 
            getElement(mat, row.name, col.index))

}
pasteSentence(mat, "b", 1)
##[1] "The element of row b and column 1 is 2"

也可以与 rowname<- b

 pasteSentence(mat, rowname, 1)
   ##[1] "The element of row b and column 1 is 2"

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