[英]Flutter/Dart group list by date
I have following list of maps,我有以下地图列表,
[
{
"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.我想操作上面的数据,使数据按它们的
DateOfBirth
分组,所以结果看起来像这样。
[
{
"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.在 Javascript 中,这可以通过使用
reduce
function 然后使用 Object 键映射来实现。 I also know dart has useful package called collection
我也知道 dart 有有用的 package 叫
collection
As I am new to dart and flutter, I am not sure how to do.由于我是 dart 和 flutter 的新手,我不知道该怎么做。 Can anybody help me on this?
有人可以帮我吗?
Thanks谢谢
You could use fold and do something like this你可以使用fold并做这样的事情
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.或者像这样,如果你想使用扩展运算符,我不知道它是否非常可读。
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();
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