I want to create a index for the following collection which will index distict keys under contexts.
```[
{
"contexts":{
"contextA": {
"value": 1
},
"contextB": {
"value": 2
}
}
},
{
"contexts": {
"contextA": {
"value": 3
},
"contextB": {
"value": 4
},
"contextC": {
"value": 4
}
}
}
]
`
in this case the above example would contain a index with the following
[
"contextA",
"contextB",
"contextC"
]
Is there a possible way to achive this ?