基於ifelse語句運行多行代碼

Question

我想根據if或ifelse語句的結果運行多行代碼。測試表達式將測試數據框中列的值。這裏是我的問題：

if語句允許當測試表達式不是一個向量只執行多個語句：

if (test_expression) { 
     statement1 
     statement2 
     statement3 
    } 

ifelse語句允許當測試表達式是一個矢量要執行一個語句：

ifelse(test_expression, statement1, statement2) 

但是，如果你想要運行在一個向量的if語句，然後運行基於結果的代碼一整節？在這個例子中，我想要運行的代碼行會生成一個圖。但實際上，我想要比這更進一步（將生成的情節作爲電子郵件附件發送）。

示例數據：

datetime <- c("12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 8:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/201610:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 10:00","12/6/2016 12:00","12/6/2016 12:00","12/6/201612:00","12/6/2016 12:00","12/6/2016 12:00","12/6/2016 12:00","12/6/2016 12:00","12/6/2016 12:00","12/6/2016 12:00","12/6/2016 12:00","12/6/2016 12:00","12/6/201612:00","12/6/2016 12:00","12/6/2016 12:00","12/6/2016 12:00") 

c <- c(2.41,1.68,2.29,2.09,3.47,2.28,2.56,2.52,2.27,1.74,2.03,2.14,2.77,2.34,1.78,2.53,2.68,2.27,1.83,1.69,1.83,2.3,2.07,1.91,2.16,3.11,2.38,2.63,2.47,2,2.35,2.11,2.03,3.2,2.17,2.58,2.64,2.23,2.12,2.17) 

elev <- c(239.5312,242.8121,246.257,249.5378,252.6874,255.7714,259.2819,262.3331,265.8436,266.8278,222.6283,226.3685,229.7806,232.9302,236.211,239.5247,242.8055,245.9223,249.3344,252.7465,256.0601,259.1441,262.5234,265.9026,266.7885,222.6513,226.3915,229.8692,232.9531,236.2012,239.6133,242.8613,246.2406,249.4558,252.7694,256.0175,259.3639,262.6448,265.86,266.8442) 

mydf <- data.frame(datetime,c,elev) 

mydf$datetime <- strptime(mydf$datetime, format = "%m/%d/%Y %H:%M") 

current.time <- "2016-12-06 12:00:00" 

current.time <- paste(format(current.time, format = "%Y-%m-%d %H"), ":00:00", sep = "") 

current.date <- "2016-12-06" 

mydf2 <- subset(mydf, datetime == current.time) 
mydf2 <- mydf2[order(-mydf2$elev),] 

例if聲明：

if(mydf2$c > 2){ 
    filename<- paste("//C:/Alert_Profile_",current.date, ".pdf", sep="") 
    pdf(filename, width=7, height=12) 
    plot(0,type="n", ylim = c(216,285), xlim= c(0,35),ylab="Elevation (ft ASL)", xlab=expression('A ('*degree*'C)')) 
    lines(mydf2$c, mydf2$elev, xaxt='n', yaxt='n', ylim = c(216,285), xlim= c(0,35), col="mediumpurple1") 
    points(mydf2$c, mydf2$elev, xaxt='n', yaxt='n', ylim = c(216,285), xlim= c(0,35), pch=21, col="black", bg= "mediumpurple1") 
    dev.off()  
    } 

Answer 1

如果你想如果一個矢量值的一個滿足條件時執行的代碼塊，有any這將如果任何值爲TRUE，則返回true。

你的if語句變成：if (any(mydf2$c > 2))

---

以前的答案可能是使用同樣的：

我會設置你的，如果條件作爲邏輯矢量：

lv <- mydf2$c > 2 

然後調用你的子集數據塊：

filename<- paste("//C:/Alert_Profile_",current.date, ".pdf", sep="") 
    pdf(filename, width=7, height=12) 
    plot(0,type="n", ylim = c(216,285), xlim= c(0,35),ylab="Elevation (ft ASL)", xlab=expression('A ('*degree*'C)')) 
    lines(mydf2$c[lv], mydf2$elev[lv], xaxt='n', yaxt='n', ylim = c(216,285), xlim= c(0,35), col="mediumpurple1") 
    points(mydf2$c[lv], mydf2$elev[lv], xaxt='n', yaxt='n', ylim = c(216,285), xlim= c(0,35), pch=21, col="black", bg= "mediumpurple1") 
    dev.off()  

或者我可能還沒有理解你在做什麼，因爲你的問題沒有提供預期的輸出，所以很難說，你的示例代碼將運行或不運行，取決於第一個值mydf2$c，並提出警告：

> d 
[1] 1 2 3 4 5 
> if (d > 3) { print("ok")} 
Warning message: 
In if (d > 3) { : 
    the condition has length > 1 and only the first element will be used