R闪亮错误：EXPR必须是长度为1的向量

Question

我正在处理已经被问到here但在服务器代码中进行了一些修改的同一个程序。这是它的更新版本：

server <- function(input, output) {
  dataset<-reactive({ 
    inFile <- input$filewav 
    dat <- read_excel(inFile$datapath)
    df <- data.frame(dat[,2], dat[,3])
    x <- seq(1,nrow(df),length = nrow(df))
    y <- df[,2]
    return(dat)
  })

  output$plot_mra <- renderPlot({
    filt <- switch(input$filterwav, 
            "Haar (d2)" = ls()[5],
            "d4" = ls()[7],
            "d6" = ls()[9],
            "d8" = ls()[11],
            "s4" = ls()[13],
            "s6" = ls()[15],
            "s8" = ls()[17],
            "c6" = ls()[3],
            "c12" = ls()[1])
    set.seed(2)
    inFile <- input$filewav 
    dat <- read_excel(inFile$datapath)
    df <- data.frame(dat[,2], dat[,3])
    x <- seq(1,nrow(df),length = nrow(df))
    y <- df[,2]
    y.mra <- mra(y,filt,input$reswav,"periodic",TRUE,"modwt")
    if(input$reswav==0)
        {plot(x,y, ylab = "", type = "p", col = "red")
        mtext("Fungsi Asli", side = 3, line = 0.1)}
    else
        mra.y <- switch(input$reswav, 
                 "1" = y.mra()@S$S1,
                 "2" = y.mra()@S$S2,
                 "3" = y.mra()@S$S3,
                 "4" = y.mra()@S$S4,
                 "5" = y.mra()@S$S5,
                 "6" = y.mra()@S$S6,
                 "7" = y.mra()@S$S7,
                 "8" = y.mra()@S$S8,
                 "9" = y.mra()@S$S9,
                 "10" = y.mra()@S$S10)
    {plot(x,y, ylab = "", type = "p", col = "red")
    par(new = TRUE)
    plot(x,mra.y, ylab = "y", xlab = "x", type = "l", col = "blue")
    mtext("Hasil Analisis Multiresolusi dengan MODWT", side = 3, line = 0.1)}
})
}

我尝试使用前面提到的shinyApp(ui = ui, server = server)链接执行这些代码和UI代码，这次我在R控制台中遇到了这个错误：

Warning: Error in switch: EXPR must be a length 1 vector
Stack trace (innermost first):
    105: excel_format
    104: read_excel_
    103: read_excel
    102: renderPlot [#25]
     92: <reactive:plotObj>
     81: plotObj
     80: origRenderFunc
     79: output$plot_mra
      4: <Anonymous>
      3: do.call
      2: print.shiny.appobj
      1: <Promise>

我可能出错的任何想法？我该怎么办呢？

更新：好的，我根据Gregor de Cillia的建议编辑了我的服务器代码。这是它的更新版本：

server <- function(input, output) {
  dataset<-reactive({ 
    inFile <- input$filewav 
    dat <- read_excel(inFile$datapath)
    df <- data.frame(dat[,2], dat[,3])
    x <- seq(1,nrow(df),length = nrow(df))
    y <- df[,2]
    return(dat)
  })

  output$plot_mra <- renderPlot({
    read_excel(req(input$filewav))
    filt <- switch(input$filterwav, 
            "Haar (d2)" = ls()[5],
            "d4" = ls()[7],
            "d6" = ls()[9],
            "d8" = ls()[11],
            "s4" = ls()[13],
            "s6" = ls()[15],
            "s8" = ls()[17],
            "c6" = ls()[3],
            "c12" = ls()[1])
    set.seed(2)
    inFile <- input$filewav 
    dat <- read_excel(inFile$datapath)
    df <- data.frame(dat[,2], dat[,3])
    x <- seq(1,nrow(df),length = nrow(df))
    y <- df[,2]
    y.mra <- mra(y,filt,input$reswav,"periodic",TRUE,"modwt")
    if(input$reswav==0)
        {plot(x,y, ylab = "", type = "p", col = "red")
        mtext("Fungsi Asli", side = 3, line = 0.1)}
    else
        mra.y <- switch(input$reswav, 
                 "1" = y.mra()@S$S1,
                 "2" = y.mra()@S$S2,
                 "3" = y.mra()@S$S3,
                 "4" = y.mra()@S$S4,
                 "5" = y.mra()@S$S5,
                 "6" = y.mra()@S$S6,
                 "7" = y.mra()@S$S7,
                 "8" = y.mra()@S$S8,
                 "9" = y.mra()@S$S9,
                 "10" = y.mra()@S$S10)
    {plot(x,y, ylab = "", type = "p", col = "red")
    par(new = TRUE)
    plot(x,mra.y, ylab = "y", xlab = "x", type = "l", col = "blue")
    mtext("Hasil Analisis Multiresolusi dengan MODWT", side = 3, line = 0.1)}
})
}

程序中似乎没有问题（basically like this），但是在我上传* .xls或* .xlsx文件（as seen here）后问题仍然存在。另外，当我尝试使用traceback()对其进行问题排查时，R的唯一回复是No traceback available。

PS：再次请原谅我的语言，我在上面的节目中使用了印度尼西亚语。