How work with one array and two react native pickers - react-native

Question

I want to use one data array for two of pickers. If one picker selected one option then I need to remove that option from other picker. I tried this from following code. I used array of length 2.
constructor(props) {
super(props);
this.state = {
startTown: 'Start Point',
endTown: 'End Point',
townList: null,
};
}
componentDidMount(){
firebase.database().ref('busRoutes').once("value",(snapshot)=>{
this.setState({townList:snapshot.val()})
})
}
<Box dir="row">
<Picker
style={{flex: 1}}
selectedValue={startTown}
onValueChange={(value) => {
this.setState({
startTown: value,
});
}}>
<Picker.Item value='Start Point' label='Start Point' />
{townList && townList.map((element,index)=>{
if(element===endTown) return;
return(<Picker.Item value={element} label={element} />)
})}
</Picker>
<Picker
style={{flex: 1}}
selectedValue={endTown}
onValueChange={(value) => {
this.setState({
endTown: value,
});
}}>
<Picker.Item value='End Point' label='End Point' />
{townList && townList.map((element,index)=>{
if(element===startTown) return;
return(<Picker.Item value={element} label={element} />)
})}
</Picker>
</Box>
But it gives error like this
length=2;index=2
here is the link to image with error.
https://imgur.com/ak3tvTB
I can`t put it here as my reputations are not enough