R Shiny error: argument “x” is missing, with no default

问题

I'm trying to make a model for non parametric regression with Maximal Overlap Discrete Wavelet Transform (MODWT) using this data taken from here and here. The packages I'm using here are shiny, wavelets, and readxl. Here is my server code:

    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)" = filter()$haar,
           "d4" = filter()$d4,
           "d6" = filter()$d6,
           "d8" = filter()$d8,
           "s4" = filter()$s4,
           "s6" = filter()$s6,
           "s8" = filter()$s8,
           "c6" = filter()$c6,
           "c12" = filter()$c12)

        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)

        set.seed(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
            {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)}
    })
    }

And here is my UI code:

    ui <- fluidPage(
      titlePanel("Pemodelan Regresi dengan Metode Wavelet Linier"),

      sidebarLayout(
        sidebarPanel(
          fileInput("filewav", "Masukkan data",
                    multiple = FALSE,
                    accept = c(".xls",".xlsx")),
        selectInput("filterwav", "Pilih filter wavelet", 
                      choices = list('Daublets' = c('Haar (d2)','d4','d6','d8'), 
                        'Symmlets' = c('s4','s6','s8'), 
                        'Coiflets' = c('c6','c12'))),
        numericInput("reswav", "Masukkan nilai resolusi", 1, min = 0, max = 10, step = NA,
      width = NULL),
          helpText("Oleh: Sania Anisa Farah")),

        mainPanel(
        plotOutput("plot_mra"))
    ))

I tried to execute those codes with shinyApp(ui = ui, server = server) and this is what I got:

    Warning: Error in as.ts: argument "x" is missing, with no default
    Stack trace (innermost first):
        104: as.ts
        103: filter
        102: renderPlot [#12]
         92: <reactive:plotObj>
         81: plotObj
         80: origRenderFunc
         79: output$plot_mra
          4: <Anonymous>
          3: do.call
          2: print.shiny.appobj
          1: <Promise>

Yes, that output in the R console and this in the program itself. Can anybody please show me where I went wrong? And how am I supposed to fix it?

PS: please excuse my language, I'm using Bahasa Indonesia in my program above.

来源：https://stackoverflow.com/questions/49206529/r-shiny-error-argument-x-is-missing-with-no-default