Flutter/Dart group list by date - flutter

Question

I have following list of maps,
[
{
"FullName":"Harry Potter",
"DateOfBirth": "2020/02/16",
"Department":"Branch Operation",
"BirthDay":"Friday"
},
{
"FullName":"John Wick",
"DateOfBirth": "2020/02/16",
"Department":"Finance",
"BirthDay":"Friday"
},
{
"FullName":"Solomon Kane",
"DateOfBirth":2020/02/19,
"Department":"Loan",
"BirthDay":"Monday"
}
]
I would like to manipulate above data such that data are grouped by their DateOfBirth, so that result would look like this.
[
{
"DateOfBirth": "2020/02/16",
"BirthDay": "Friday",
"Data":[
{
"FullName": "Harry Potter",
"Department":"Branch Operation",
},
{
"FullName":"John Wick",
"Department":"Finance",
}
]
},
{
"DateOfBirth": "2020/02/19",
"BirthDay": "Monday",
"Data":[
{
"FullName":"Solomon Kane",
"Department":"Loan"
}
]
},
]
In Javascript, this can be achieved by using reduce function and then using Object key mapping.
I also know dart has useful package called collection
As I am new to dart and flutter, I am not sure how to do. Can anybody help me on this?
Thanks

Answer 1

You could use fold and do something like this
const data = [...];
void main() {
final value = data.fold(Map<String, List<dynamic>>(), (Map<String, List<dynamic>> a, b) {
a.putIfAbsent(b['DateOfBirth'], () => []).add(b);
return a;
}).values
.where((l) => l.isNotEmpty)
.map((l) => {
'DateOfBirth': l.first['DateOfBirth'],
'BirthDay': l.first['BirthDay'],
'Data': l.map((e) => {
'Department': e['Department'],
'FullName': e['FullName'],
}).toList()
}).toList();
}
Or like this if you want to use the spread operator, I don't know if its very readable though.
final result = data.fold({}, (a, b) => {
...a,
b['DateOfBirth']: [b, ...?a[b['DateOfBirth']]],
}).values
.where((l) => l.isNotEmpty)
.map((l) => {
'DateOfBirth': l.first['DateOfBirth'],
'BirthDay': l.first['BirthDay'],
'Data': l.map((e) => {
'Department': e['Department'],
'FullName': e['FullName'],
}).toList()
}).toList();