Reduce the number of if statements in R

I have a function to clear my data and keep only the observations that I want but that includes many if statements. I have an order for the codes I want to keep by id.

clear.data = function(x)
{  
  A = unique(x$code)

  if (4 %in% A  )
  {x = subset(x,code==4)}
  else if (10404 %in% A)
  {x = subset(x,code==10404)}
  else if (3942 %in% A)
  {x = subset(x,code==3942)}

  else {x=x}

  return(x)
}

For example in the data x

x = data.frame(id = c("A","A", "A", "B", "B","B", "B","C","C", "C","C"), 
               date = c( "29/05/2013", "23/08/2011", "25/09/2011",  "18/11/2011", "10/07/2013", "04/10/2011", "10/11/2011",  
                         "15/12/2011", "10/02/2008", "07/09/2009", "22/03/2012" ),
               code = c(4,4,3942,4,10404,3942,10404,10404,3942,10404,3942)      )

I will use lapply to keep only the observations by person I am interested

> lapply(split(x,x$id),clear.data)
$A
  id       date code
1  A 29/05/2013    4
2  A 23/08/2011    4

$B
  id       date code
4  B 18/11/2011    4

$C
   id       date  code
8   C 15/12/2011 10404
10  C 07/09/2009 10404

The problem is that I have 150 codes so that's a lot of if statements and a large dataset to apply my function. Is there a way to reduce the if statements somehow? I busted my head in order to find a solution and have searched a lot but couldn't find anything. Do you have any ideas? Many thanks