Create multiple rows in table based on multi-select dropdown

[I_like_R]

Hello,

I am building a Shiny app with 2 tabs. The first tab contains 2 multi-select dropdown menus. The 2nd tab contains a table that is filtered/impacted by the selections of the 2 dropdowns from the previous tab. The first dropdown filters the table. The second dropdown is a little different: I want the selections in the 2nd dropdown to all populate in their respective column in the table on the 2nd tab. Further, I would like an additional row to be created for each additional selection beyond the 1st selection. For example, if I had a dataset like the following:

Col1    Col2     Col3
1       a        Group1      
2       a        Group2
3       b        Group3
4       b        Group2
5       b        Group3
6       b        Group2
7       a        Group2

Let's say the first dropdown filters Col2 and I only want to see values = a. Then, we have:

Col1    Col2     Col3
1       a        Group1      
2       a        Group2
7       a        Group2

Next, I want the 2nd dropdown to able to select any of Groups 1, 2, or 3 from Col3 regardless of what is left after the first filtering step. So, if I select Group 1 and Group 3 from the dropdown on the previous tab - I want the # of rows to double. So, it would essentially look like this:

Col1    Col2     Col3
1       a        Group1     
1       a        Group3     
2       a        Group1
2       a        Group3
7       a        Group1
7       a        Group3

Here is some example code I've started on:

#----- Load libraries -----#
library(shiny)
library(shinydashboard)
library(DT)
library(shinyWidgets)
library(dplyr)
library(rhandsontable)

# Define UI for application 

ui <- fluidPage(
  dashboardPage(
    dashboardHeader(title="Draft"),
    dashboardSidebar(
      sidebarMenu(
        menuItem("Filtering Questions",
                 tabName = "questions",
                 icon = icon('question')
        ),
        menuItem("All Data",
                 tabName = "all_data",
                 icon=icon("table")
        )
      )
    ),
    dashboardBody(
      tabItems(
        tabItem(
          tabName = "questions",
          selectInput(
            inputId = 'q1',
            label = '1.) Choose carb',
            choices = unique(mtcars$carb),
            selected = unique(mtcars$carb)[1],
            multiple = TRUE
          ),
          br(),
          selectInput(
            inputId = 'q2',
            label = '2.) Choose gear',
            choices = unique(mtcars$gear),
            selected = unique(mtcars$gear)[1],
            multiple = TRUE
        )),
        tabItem(
          tabName = "all_data",
          rHandsontableOutput("all_table")
        )
      ))))

# Define server logic 
server <- function(input, output) {
  
  mtcars_filter = reactive({
    filter = subset(mtcars,carb %in% input$q1)
    
    #Add in value(s) selected for gear --> will create 1, 2, or 3 possible rows per indicator
    
    return(filter)
  })
  
  #----------All Data Table----------#
  output$all_table=renderRHandsontable({
    
    
    my_table = rhandsontable(mtcars_filter()) %>%
      hot_col(c(1:11), readOnly = TRUE) %>%
      hot_context_menu(allowRowEdit = FALSE, allowColEdit = FALSE) %>%
      hot_table(highlightCol = TRUE, highlightRow = TRUE)
    
    return(my_table)
    
  })
}

# Run the application 
shinyApp(ui = ui, server = server)

How do I implement this logic to add rows based on the dropdown selections? Not sure how to incorporate this logic. Any help would be appreciated! Thank you!