用ggplot2繪製多個ROC曲線在不同的層

Question

我想繪製與ggplot2在一個繪圖上的多個ROC曲線。下面是我在多大程度上得到：

ggroc2 <- function(columns, data = mtcars, classification = "am", 
        interval = 0.2, breaks = seq(0, 1, interval)){ 
    require(pROC) 
    require(ggplot2) 

    #The frame for the plot 
    g <- ggplot() + geom_segment(aes(x = 0, y = 1, xend = 1,yend = 0)) + 
    scale_x_reverse(name = "Specificity",limits = c(1,0), breaks = breaks, 
expand = c(0.001,0.001)) + 
    scale_y_continuous(name = "Sensitivity", limits = c(0,1), breaks = 
breaks, expand = c(0.001, 0.001)) + 
    theme_classic() + coord_equal() 

    #The loop to calculate ROC's and add them as new layers 
    for(i in 1:length(columns)){ 
    croc <- roc(data[,classification], data[,columns[i]]) 
    plotx <- rev(croc$specificities) 
    ploty <- rev(croc$sensitivities) 
    g <- g + geom_step(aes(x=plotx, y=ploty)) 
    } 

    g 
} 



#Sample graph 
ggroc2(c("mpg", "disp", "drat", "wt")) 

的問題是，只有在columns列表中的最後一個參數被繪製。我發現問題必須與aes()有關，並在閱讀the answer to this question後進行懶惰評估。該示例使用geom_segment()，並且在完全刪除aes()後問題得到解決。它不適合我，因爲我需要以某種方式映射數據。當我在這裏刪除aes()時，沒有任何東西被繪製。如何解決geom_中依賴於aes()的懶惰評估問題？

Answer 1

這是您的代碼的工作版本。
最終的圖形結果不是很好，應該改進。

ggroc2 <- function(columns, data = mtcars, classification = "am", 
        interval = 0.2, breaks = seq(0, 1, interval)){ 
    require(pROC) 
    require(ggplot2) 

    #The frame for the plot 
    g <- ggplot() + geom_segment(aes(x = 0, y = 1, xend = 1,yend = 0)) + 
    scale_x_reverse(name = "Specificity",limits = c(1,0), breaks = breaks, 
expand = c(0.001,0.001)) + 
    scale_y_continuous(name = "Sensitivity", limits = c(0,1), breaks = 
breaks, expand = c(0.001, 0.001)) + 
    theme_classic() + coord_equal() 

    #The loop to calculate ROC's and add them as new layers 
    cols <- palette() 
    for(i in 1:length(columns)){ 
    croc <- roc(data[,classification], data[,columns[i]]) 
    sens_spec <- data.frame(spec=rev(croc$specificities), 
          sens=rev(croc$sensitivities)) 
    g <- g + geom_step(aes(x=spec, y=sens), data=sens_spec, col=cols[i], lwd=1) 
    } 
    g 
} 

#Sample graph 
ggroc2(c("mpg", "disp", "drat", "wt"))