问题描述
这真的挑战了我调试R代码的能力。
我想用的组合来完成这项工作。
code>和调用在 NewColName 仍然可见的环境中构建调用:myFunction< - function(x,y){
NewColName< - a
z< - do .call(ddply,list(x,y,summarize,Ave = call(mean,as.symbol(NewColName),na.rm = TRUE)))
return(z)
}
myFunction(df,sv)
b Ave
1 0 1.5
2 1 3.5
This has really challenged my ability to debug R code.
I want to use ddply() to apply the same functions to different columns that are sequentially named; eg. a, b, c. To do this I intend to repeatedly pass the column name as a string and use the eval(parse(text=ColName)) to allow the function to reference it. I grabbed this technique from another answer.
And this works well, until I put ddply() inside another function. Here is the sample code:
# Required packages: library(plyr) myFunction <- function(x, y){ NewColName = "a" z = ddply(x, y, summarize, Ave = mean(eval(parse(text=NewColName)), na.rm=TRUE) ) return(z) } a = c(1,2,3,4) b = c(0,0,1,1) c = c(5,6,7,8) df = data.frame(a,b,c) sv = c("b") #This works. ColName = "a" ddply(df, sv, summarize, Ave = mean(eval(parse(text=ColName)), na.rm=TRUE) ) #This doesn't work #Produces error: "Error in parse(text = NewColName) : object 'NewColName' not found" myFunction(df,sv) #Output in both cases should be # b Ave #1 0 1.5 #2 1 3.5
Any ideas? NewColName is even defined inside the function!
I thought the answer to this question, loops-to-create-new-variables-in-ddply, might help me but I've done enough head banging for today and it's time to raise my hand and ask for help.
You can do this with a combination of do.call and call to construct the call in an environment where NewColName is still visible:
myFunction <- function(x,y){ NewColName <- "a" z <- do.call("ddply",list(x, y, summarize, Ave = call("mean",as.symbol(NewColName),na.rm=TRUE))) return(z) } myFunction(d.f,sv) b Ave 1 0 1.5 2 1 3.5
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