当列可能不存在时用 $ 进行子集化

问题描述：

我正在编写一个由 ifelse 语句组成的函数，该函数依赖于作为函数输入的不同列中的值:

I am writing a function made up of ifelse statements that depends on values in different columns of the that are the function's input:

counter=function(df){
df$total2=ifelse(df$x>=100,df$total+10,df$total)
df$total3=ifelse(df$y>=200,df$total2+10,df$total2)
}

看起来我这样做的方式效率很低，但我还没有想到避免覆盖计算的方法.

It seems like the way I'm doing it is quite inefficient, but I haven't thought of a way to avoid overwriting the calculations.

但更紧迫的是，我想使用这个函数的一些 dfs 没有 x 列和 y 列.当我在这些上运行它时，会出现以下错误；

But more pressingly, some of the dfs I'd like to use this function on do not have both column x and column y. When I run it on these, the following error sappears;

$<-.data.frame(*tmp*, "total3", value = logical(0)) 中的错误:替换有 0 行，数据有 74

Error in $<-.data.frame(*tmp*, "total3", value = logical(0)) : replacement has 0 rows, data has 74

有没有办法重写它以允许没有所有列的数据框?

Is there a way to rewrite this to allow for dataframes that don't have all of the columns?

谢谢.

答

你可以使用标准的if来查看列是否存在

You can just use a standard if to see if a column exists

counter <- function(df) {
    if ("x" %in% names(df) ) {
        df<- transform(df, total2=ifelse(x>=100,total+10,total)
    }
    if("y" %in% names(df) ) {
        df <- transform(df, total3=ifelse(y>=200,total2+10,total2)
    }
}

虽然看起来您的数据可能采用宽"格式，但以高"格式处理可能更容易.您可能想考虑重塑您的数据.

Though it seems like your data might be in a "wide" format when it may be easier to work with in the a "tall" format. You might want to look into reshaping your data.

当列可能不存在时用 $ 进行子集化

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