Error "arguments imply differing number of rows" when subsetting data with Shiny/ggplot2

Question

I am afraid I am stuck.

I have a simple Shiny script with the intention of subsetting a dataframe based on user input and plot two variables in a scatterplot. When running the script I always get the error "Error in data.frame(x = c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, : arguments imply differing number of rows: 1786, 2731". All I know is this error occurs when data is n_col!=n_row in a dataframe. However, I do not see how this can be the issue here. What buffles me is, if I execute the snippet below , the plot is drawn without problems:

#test4 <- subset(test2, grepl("PLANT1", test2$PLANTS))
#ggplot(test4, aes(x=test4$HOUR, y=test4$PRICE_NO)) +
     geom_point(shape=1)

All I am doing is substituting the string with input$plant from ui.r.

Here is my Main window code:

###################################
# Launch  App
###################################
#install.packages("shiny")
#install.packages("ggplot2")
library(shiny)
library(ggplot2)

#load data
#data <- read.csv2(file="C:/data.csv",head=FALSE)
#test4 <- subset(test2, grepl("PLANT1", test2$PLANTS))
#ggplot(test4, aes(x=test4$HOUR, y=test4$PRICE_NO)) +
     geom_point(shape=1)

runApp("C:/PATH/")

My server.r

library(shiny)
library(ggplot2)

# Define Input to Plot
shinyServer(function(input, output) {

output$distPlot <- renderPlot({
# Draw Plot
test4 <- subset(test2, grepl(input$plant, test2$PLANTS))
ggplot(test4, aes(x=test4$HOUR, y=test4$PRICE_NO)) +
  geom_point(shape=1)
})
})

My ui.r

library(shiny)

# Title
shinyUI(fluidPage(

titlePanel("TITLE"),

#Sidebar Layout
sidebarLayout(
 sidebarPanel(
  textInput("plant",
              label = h3("Plant:"),
              value = "PLANT1")
  ),

#
mainPanel(
  plotOutput("distPlot")
  )
)

))

Sample data as requested:

test2

plants HOUR PRICE

plant1 1    12,45
plant1 2    15,52
plant1 3    15,45
plant1 4    78,12
plant1 5    72,12
plant2 1    78,72
plant2 2    72,52
plant2 3    75,52 
plant2 4    78,11

Please provide a sample data so that we can reproduce your error. Also, avoid using subset for the reason mentioned here — user227710
– user227710, Commented Jun 21, 2015 at 13:26
Provided sample data and replaced substitute() with test4 <- test2[test2$UNIT_REFERENCE_NO == input$plant,]. Whoever, no effect on the issue. I can see the problem is with ggplot, but I fail to see why. — lammy
– lammy, Commented Jun 21, 2015 at 13:44
Please check my answer. You are not correctly using grepl here (at least to your sample data). — user227710
– user227710, Commented Jun 21, 2015 at 13:51

user227710 · Accepted Answer · 2015-06-21 13:50:42Z

Conditional on what I mentioned in the comment regarding the use of subset, you can proceed as follows (you don't need to use grepl here)

test4 <- subset(test2, test2$plants==input$plant)
    ggplot(test4, aes(x=HOUR, y=PRICE)) +
      geom_point(shape=1)

ui. R

library(shiny)

# Title
shinyUI(fluidPage(

  titlePanel("TITLE"),

  #Sidebar Layout
  sidebarLayout(
    sidebarPanel(
      selectInput("plant",
                label = h3("Plant:"),
                choices = c("plant1","plant2"),
                selected="plant1")
    ),

    #
    mainPanel(
      plotOutput("distPlot")
    )
  )
))

server.R

library(shiny)
library(ggplot2)

test2<-readRDS("data\\test2.rds")

# Define Input to Plot

shinyServer(function(input, output) {

  output$distPlot <- renderPlot({
    # Draw Plot
    test4 <- subset(test2, test2$plants==input$plant)
    ggplot(test4, aes(x=HOUR, y=PRICE)) +
      geom_point(shape=1)
  })
})

Your sample data which is in data folder inside the app:

test2<-structure(list(plants = structure(c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 
2L, 2L), .Label = c("plant1", "plant2"), class = "factor"), HOUR = c(1L, 
2L, 3L, 4L, 5L, 1L, 2L, 3L, 4L), PRICE = structure(c(1L, 3L, 
2L, 8L, 4L, 9L, 5L, 6L, 7L), .Label = c("12,45", "15,45", "15,52", 
"72,12", "72,52", "75,52", "78,11", "78,12", "78,72"), class = "factor")), .Names = c("plants", 
"HOUR", "PRICE"), class = "data.frame", row.names = c(NA, -9L
))

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