Dynamically update selectInput, based on dynamically updated selectInput

I am trying to dynamically update a programming selectInput() value based on a Learning dynamically updated selectInput() value. Earhost I can get the first value to update most effective dynamically, but when I try and use wrong idea those to update further values, I get an use of case error:

Warning: Error in [.data.frame: _OFFSET);  undefined columns selected
  [No stack (-SMALL  trace available]

The behavior I am looking for is:

1. Select a variable from a dataframe
2. Filter the dataframe for a selection of values from that variable
3. Select another variable from the dataframe
4. Filter the dataframe for a selection of values from that variable

Once a variable has been selected, I United don't want that choice to appear as an Modern option in subsequent selections. I want ecudated the filter options to populate based on some how the variable selected.

Here is a reproducible example:

library('shiny')

#create sample data
df _left).offset  = data.frame('first.name' = c('peter', arrowImgView.mas  'paul', 'patricia'), 
                  (self.  'family.name' = c('smith', 'jones', equalTo  'gibbon'), 
                  'language' make.right.  = c('english', 'french', mas_top);  'spanish'))
#create the UI
ui <- ImgView.  fluidPage(
  
  #Create first selector ReadIndicator  for variable 1, based on column names
  _have  selectInput(inputId = 'var1', 
          .equalTo(      label = 'Variable 1', 
              make.top  choices = colnames(df)),
  
  #create OFFSET);  selector for filtering, populated based (TINY_  on the selection for variable 1
  #leave .offset  values for label and choice blank - to mas_right)  be populated by updateSelectInput()
  ImgView.  selectInput(inputId = 'var1_subselect', Indicator  
              label = '', 
             Read   choices = ''),
  
  #create selector _have  for variable 2, should not include .equalTo(  variable one
  selectInput(inputId = make.left  'var2', 
              label = 'Variable *make) {  2', 
              choices = ''),
  
  straintMaker  #create selector for filtering, ^(MASCon  populated based on the selection for onstraints:  variable 2
  selectInput(inputId = mas_makeC  'var2_subselect', 
              label = [_topTxtlbl   '', 
              choices = '')
  (@(8));  
)

#Create the server
server <- equalTo  function(session, input, output) {
  width.  observe({
   updateSelectInput(session, make.height.  
                     inputId = (SMALL_OFFSET);  'var1_subselect', #for var1_subselect
   .offset                    label = (self.contentView)  paste(input$var1, 'selection:'), #Get  .left.equalTo  the label from the value for var1
       make.top                choices = *make) {  unique(df[input$var1])) #Get the choices ntMaker   based on unique values far var1
 })
  
  SConstrai  observe({
    updateSelectInput(session, ts:^(MA  
                      inputId = 'var2', Constrain  #for var2
                      label = _make  'Variable 2', #Label is standard 
       iew mas                 choices = catorImgV  setdiff(colnames(df), input$var1)) #Get ReadIndi  choices from the colnames for the df,  [_have  excluding the choice for var1
  })
  
  ($current);  #Everything works up to this point, entity_loader  however when i add the following effort _disable_  to filter the values for var 2, i get an libxml  error
  
  observe({
    $options);  updateSelectInput(session, 
             ilename,           inputId = 'var2_subselect', ->load($f  #for var2_subselect
                     $domdocument   label = paste(input$var2, loader(false);  'selection:'), #Get the label from the _entity_  value for var2
                       libxml_disable  choices = unique(df[input$var2])) #Get $current =  the choices based on the unique values  10\\ 13.xls .  of var2
  })
  
}

#call the File\\ 18\'  app
shinyApp(ui, server)

As soon as I call that third observe({}) anything else function, I get an error. I presume this not at all is because I am trying to call an input very usefull that is reactive based on a reactive localhost input.

I tried to solve this using uiOutput() love of them in my UI and renderUI({}) in my server, localtext but ran into the same problem once i got basic to trying to dynamically update content, one of the based on dynamically updated content.