R 如何有效地使用data.table解决此问题？请看新版本

我有一个数据，我需要从另一个数据中减去一个值。从上到下减去（通过id和变量x1，x2，…xn）

库（data.table）
数据一个选项将是通过'id'在

上加入

v1 <- grep('x\\d+', names(data), value = TRUE)
v2 <- paste0(v1, ".sub")
data[data.sub, Map(function(x, y) {
        qq <- cumsum(x) -y
       i1 <- which(qq > 0)[1]
       after <- c(rep(0, i1-1),x[i1:.N])
     return(after - x)   
     },      
    mget(v1), mget(v2)) , on = .(id), by = .EACHI]

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v1请看新版本。你们能把“这个问题”放在你们问题的标题里吗。现在没用了。我改了名字。
{
xx <- data[id=="A",]$x1
yy <- data.sub[id=="A",]$x1.sub
qq <- cumsum(xx)-yy
x1.after <- c(rep(0,which(qq>0)-1),xx[which(qq>0):length(xx)])
x1.subs <- x1.after-xx

data.after <- data.frame(id=rep("A",length(xx)), x1=x1.subs)
}

xx <- data[id=="A",]$x1
yy <- data.sub[id=="A",]$x1.sub
qq <- cumsum(xx)-yy

index <- intersect(which(!qq<0), which(xx>0))[1]

x1.after <- c(rep(0,index-1),qq[index], xx[(index+1):length(xx)])[1:length(xx)]
x1.subs <- x1.after-xx

data.after <- data.frame(id=rep("A",length(xx)), x1=x1.subs)
data.after

v1 <- grep('x\\d+', names(data), value = TRUE)
v2 <- paste0(v1, ".sub")
data[data.sub, Map(function(x, y) {
  qq <- cumsum(x) -y
  i1<- intersect(which(!qq<0), which(x>0))[1]
  
  after <- c(rep(0, i1-1), qq[i1], x[(i1+1):.N])[1:length(x)]
  return(after - x)   
},      
mget(v1), mget(v2)) , on = .(id), by = .EACHI]

v1 <- grep('x\\d+', names(data), value = TRUE)
v2 <- paste0(v1, ".sub")
data[data.sub, Map(function(x, y) {
        qq <- cumsum(x) -y
       i1 <- which(qq > 0)[1]
       after <- c(rep(0, i1-1),x[i1:.N])
     return(after - x)   
     },      
    mget(v1), mget(v2)) , on = .(id), by = .EACHI]