缩短嵌套ifelse [英] Shorten nested ifelse
本文介绍了缩短嵌套ifelse的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
如果给出了以下数据表，因此我们希望将x1与x2和x5进行比较，则可以使用以下内容：
If the following data table is given, and we would like to compare x1 consequently with x2 to x5, the following can be used:
set.seed(1)
library(data.table)
TDT <- data.table(x1 = round(rnorm(100,0.75,0.3),2),
x2 = round(rnorm(100,0.75,0.3),2),
x3 = round(rnorm(100,0.75,0.3),2),
x4 = round(rnorm(100,0.75,0.3),2),
x5 = round(rnorm(100,0.75,0.3),2))
TDT[,compare := ifelse(x1 < x2,1,ifelse(x1 < x3,2,ifelse(x1 < x4,3,ifelse(x1 < x5,4,5))))]
因此，如果 x1< x2 ，然后 compare == 1 ，依此类推。
So if x1 < x2, then compare == 1, etc.
在我的示例中，我有很多专栏可以比较x1。有什么方法可以更简洁地编写此代码，即没有嵌套的ifelse吗？
Now in my example, I have a lot more columns to compare x1 with. Is there any way to write this more concisely, i.e. without nested ifelse?
推荐答案
我们可以使用 data.table
TDT[, compare := {d1 <- as.data.table(Map(function(x) x1 < x, .SD))
max.col(d1, "first") *(c(5, 1)[((Reduce(`+`, d1)!=0)+1)])}, .SDcols = x2:x5]
#OP's code
v1 <- TDT[, ifelse(x1 < x2,1,ifelse(x1 < x3,2,ifelse(x1 < x4,3,ifelse(x1 < x5,4,5))))]
identical(v1, TDT$compare)
#[1] TRUE
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