javascript 使用 lodash 嵌套 _.max()
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Nested _.max() with lodash
提问by Sergei Basharov
I am trying to get max and min values of arrays values inside objects array which looks like this:
我试图在对象数组中获取数组值的最大值和最小值，如下所示：
[
{
id: 1,
enabled: false,
layer: 'Mood',
color: '#f16c63',
points: [
{date: '2013-01-02', value: 20},
{date: '2013-02-02', value: 15},
{date: '2013-03-12', value: 24},
{date: '2013-03-23', value: 18},
{date: '2013-03-24', value: 22},
{date: '2013-04-09', value: 12},
{date: '2013-06-13', value: 16},
{date: '2013-06-14', value: 20},
]
},
{
id: 2,
enabled: true,
layer: 'Performance',
color: '#698bfc',
points: [
{date: '2013-01-02', value: 15},
{date: '2013-02-02', value: 24},
{date: '2013-03-12', value: 29},
{date: '2013-03-23', value: 21},
{date: '2013-03-24', value: 20},
{date: '2013-04-09', value: 17},
{date: '2013-06-13', value: 25},
{date: '2013-06-14', value: 21},
]
},
{
id: 3,
enabled: false,
layer: 'Fatigue',
color: '#e1fc6a',
points: [
{date: '2013-01-02', value: 32},
{date: '2013-02-02', value: 27},
{date: '2013-03-12', value: 30},
{date: '2013-03-23', value: 31},
{date: '2013-03-24', value: 27},
{date: '2013-04-09', value: 15},
{date: '2013-06-13', value: 20},
{date: '2013-06-14', value: 18},
]
},
{
id: 4,
enabled: true,
layer: 'Hunger',
color: '#63adf1',
points: [
{date: '2013-01-02', value: 12},
{date: '2013-02-02', value: 15},
{date: '2013-03-12', value: 13},
{date: '2013-03-23', value: 17},
{date: '2013-03-24', value: 10},
{date: '2013-04-09', value: 14},
{date: '2013-06-13', value: 12},
{date: '2013-06-14', value: 11},
]
},
]
I need to get the max and the min values from the pointsarrays.
Seems like I can do something like this for max and similar for min values:
我需要从points数组中获取最大值和最小值。似乎我可以对最大值执行类似的操作，对最小值执行类似的操作：
var maxDate = _.max(dataset, function (area) {
return _.max(area.points, function (point) {
console.log(new Date(point.date).getTime())
return new Date(point.date).getTime()
})
});
But for some reason this returns me -Infinity. Is it legit at all to use nested _.max() runs? I used this approach with D3.js library which worked just fine.
但出于某种原因，这使我返回-Infinity。使用嵌套的 _.max() 运行是否合法？我将这种方法与 D3.js 库一起使用，效果很好。
Please advise.
请指教。
回答by JLRishe
The inner _.maxis going to return the point with the maximum date, but the function you're passing to the outer _.maxexpects a value that can be compared. When it compares those values, it will return the layer with the maximum value.
内部_.max将返回具有最大日期的点，但您传递给外部的函数_.max需要一个可以比较的值。当它比较这些值时，它将返回具有最大值的图层。
It sounds like you want to get the maximum point out of all the available layers (is this right)?
听起来您想从所有可用层中获得最大点（对吗）？
If so, you can do this:
如果是这样，您可以这样做：
function pointDate(point) {
console.log(new Date(point.date).getTime())
return new Date(point.date).getTime()
}
var maxDate = _.max(_.map(dataset, function (area) {
return _.max(area.points, pointDate);
}), pointDate);
This will return the point object with the maximum date across all points.
这将返回所有点中具有最大日期的点对象。
Here's a nice functional-style approach:
这是一个很好的函数式方法：
function pointDate(point) {
console.log(new Date(point.date).getTime())
return new Date(point.date).getTime()
}
var maxDate = _(dataset).map('points').flatten().max(pointDate);
回答by Lorand-Edmond Iszlai
You can use _.maxBy from lodash, (max and maxBy)it compares date type without the need of transfor them with .getTime().
您可以使用 lodash 中的 _.maxBy，（max 和 maxBy）它比较日期类型而无需使用 .getTime() 转换它们。
