flat static method
Implementation
static Map<String,dynamic> flat(Map<String,dynamic>d){
final r=<String,dynamic>{};
d.forEach((k, v) {
if(v is List&&v.isNotEmpty&&v[0]is Map){
int i=0;
v.cast<Map<String,dynamic>>().forEach((e) {
e.forEach((km, vm) {r[makeNestedKey(k,km,i)]=vm; });
i++;
});
}else r[k]=v;
});
return r;
}