grouping launch file

edit

Hi everyone, I need to start different nodes in the launch file. At the moment I do it by defining 2 arguments (var1 and var2) and then by grouping the launch files. Something like:

<group if="$(arg var1)"> 
   start some nodes
</group>

<group if="$(arg var2)">
  start  other nodes
</group>

and launching from terminal the following:

roslaunch my_package my_launch_file var1:=true var2:=false

This works, but my question is: is there a way I could launch by defining only one arg? For example what I want to achieve is:

<arg name="variable"/> 

    <group if=**(variable=1)**>        --> How can I implement this?
    start some nodes
        </group>

        <group if=(variable=2)>
start other nodes
        </group>

and therefore using from terminal only:

roslaunch my_package launch_file variable:=1

or

roslaunch my_package launch_file variable:=2