从数组中获取元素，直到条件匹配

Question

I have an array like this

var arr = [
    "/a_3312368_392921_800MHz", 
    "/a_3312368_392853_900MHz", 
    "/a_3312368_578261_1GHz", 
    "/a_3312368_578189_120GHz", 
    "/a_3312368_578167_140GHz", 
    "/a_3312368_578230_160GHz", 
    "/a_3312368_578192_180GHz", 
    "/a_3312368_397393_183GHz", 
    "/a_3312368_582870_186GHz", 
    "/a_3312368_578174_190GHz", 
    "/a_3312368_578177_2GHz", 
    "/a_3312368_578922_210GHz", 
    "/a_3312368_578479_220GHz", 
    "/a_3312368_578357_226GHz", 
    "/a_3312368_578182_240GHz", 
    "/a_3312368_578919_250GHz", 
    "/a_3312368_578349_253GHz", 
    "/a_3312368_578639_280GHz", 
    "/a_3312368_579178_3GHz"
];

I need to get value on an operator selection. I have some operators like this

`> , < , = , <= , >=`

And here is the selected value for example

var selection = "/a_3312368_578189_120GHz";

My current operator for instance

var operator = ">";

This is some code i have written.

var string_array = [];
for(var i = 0; i < arr.length; i++){
    if(selection == arr[i]){
        break;
    }
    string_array.push(arr[i]);
}
console.log(string_array);

It is giving me proper results. But when i am trying it with map it produces error Can't have break outside of loop .

string_array = arr.map(function(item) {  if (selection == item){ break; }  else {return item;} });

How can i write a one line code for this.

Fiddle Link

Answer 1

Well… you can't break map. Don't use map . Use some or every .

Example - some: - some will break when the callback returns true

arr.some(function (item) {if (selection == item) {return true;}});    

 var selection = "/a_3312368_578189_120GHz"; var arr = ["/a_3312368_392921_800MHz", "/a_3312368_392853_900MHz", "/a_3312368_578261_1GHz", "/a_3312368_578189_120GHz", "/a_3312368_578167_140GHz", "/a_3312368_578230_160GHz", "/a_3312368_578192_180GHz", "/a_3312368_397393_183GHz", "/a_3312368_582870_186GHz", "/a_3312368_578174_190GHz", "/a_3312368_578177_2GHz", "/a_3312368_578922_210GHz", "/a_3312368_578479_220GHz", "/a_3312368_578357_226GHz", "/a_3312368_578182_240GHz", "/a_3312368_578919_250GHz", "/a_3312368_578349_253GHz", "/a_3312368_578639_280GHz", "/a_3312368_579178_3GHz" ]; string_array = []; arr.some(function(item) { if (selection == item){ return true; }else{string_array.push(item);} }); console.log(string_array); 

Example-every: - every will break when the callback returns false

arr.every(function(item) { if (selection == item) {return false;}});  

 var selection = "/a_3312368_578189_120GHz"; var arr = ["/a_3312368_392921_800MHz", "/a_3312368_392853_900MHz", "/a_3312368_578261_1GHz", "/a_3312368_578189_120GHz", "/a_3312368_578167_140GHz", "/a_3312368_578230_160GHz", "/a_3312368_578192_180GHz", "/a_3312368_397393_183GHz", "/a_3312368_582870_186GHz", "/a_3312368_578174_190GHz", "/a_3312368_578177_2GHz", "/a_3312368_578922_210GHz", "/a_3312368_578479_220GHz", "/a_3312368_578357_226GHz", "/a_3312368_578182_240GHz", "/a_3312368_578919_250GHz", "/a_3312368_578349_253GHz", "/a_3312368_578639_280GHz", "/a_3312368_579178_3GHz" ]; string_array = []; arr.every(function(item) {if (selection != item){string_array.push(item);} return item.indexOf(selection) == -1; }); console.log(string_array); 

Answer 2

When you use map result array have same element count as source.
What you want is just filter array, so use filter function.

Also if your source array sorter, so operator just show relation with index of selected element.

So your code should be like this

var selection = "/a_3312368_578189_120GHz";
var indexSelected = arr.indexOf(selection)
string_array = arr.filter(function(el, index){
    return index < indexSelected;
});

 var arr = [ "/a_3312368_392921_800MHz", "/a_3312368_392853_900MHz", "/a_3312368_578261_1GHz", "/a_3312368_578189_120GHz", "/a_3312368_578167_140GHz", "/a_3312368_578230_160GHz", "/a_3312368_578192_180GHz", "/a_3312368_397393_183GHz", "/a_3312368_582870_186GHz", "/a_3312368_578174_190GHz", "/a_3312368_578177_2GHz", "/a_3312368_578922_210GHz", "/a_3312368_578479_220GHz", "/a_3312368_578357_226GHz", "/a_3312368_578182_240GHz", "/a_3312368_578919_250GHz", "/a_3312368_578349_253GHz", "/a_3312368_578639_280GHz", "/a_3312368_579178_3GHz" ]; var selection = "/a_3312368_578189_120GHz"; var indexSelected = arr.indexOf(selection); var string_array = arr.filter(function(el,index){ return index < indexSelected; }); document.getElementById('r').innerHTML = JSON.stringify(string_array,null, 2); 

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As say @Toffy in comment - in your case, seems, you need simple slice

var indexSelected = arr.indexOf(selection)
string_array = arr.slice(0,indexSelected);

 var arr = [ "/a_3312368_392921_800MHz", "/a_3312368_392853_900MHz", "/a_3312368_578261_1GHz", "/a_3312368_578189_120GHz", "/a_3312368_578167_140GHz", "/a_3312368_578230_160GHz", "/a_3312368_578192_180GHz", "/a_3312368_397393_183GHz", "/a_3312368_582870_186GHz", "/a_3312368_578174_190GHz", "/a_3312368_578177_2GHz", "/a_3312368_578922_210GHz", "/a_3312368_578479_220GHz", "/a_3312368_578357_226GHz", "/a_3312368_578182_240GHz", "/a_3312368_578919_250GHz", "/a_3312368_578349_253GHz", "/a_3312368_578639_280GHz", "/a_3312368_579178_3GHz" ]; var selection = "/a_3312368_578189_120GHz"; var indexSelected = arr.indexOf(selection); var string_array = arr.slice(0,indexSelected); document.getElementById('r').innerHTML = JSON.stringify(string_array,null, 2); 

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Sample if source array not sorted

var selection = "/a_3312368_578189_120GHz";
var selectedFreq = getFreq(selection);

function getFreq(s) {
    var parts = s.match(/(\d+)(MHz|GHz)$/);
    return parts[1]* (parts[2] == "GHz" ? 1000: 1);    
}
var string_array = arr.filter(function(el) {
    var elFreq = getFreq(el);
    return selectedFreq > elFreq;
});

 var arr = [ "/a_3312368_392921_800MHz", "/a_3312368_392853_900MHz", "/a_3312368_578261_1GHz", "/a_3312368_578922_210GHz", "/a_3312368_578479_220GHz", "/a_3312368_578357_226GHz", "/a_3312368_578182_240GHz", "/a_3312368_578919_250GHz", "/a_3312368_578349_253GHz", "/a_3312368_578639_280GHz", "/a_3312368_579178_3GHz", "/a_3312368_578189_120GHz", "/a_3312368_578167_140GHz", "/a_3312368_578230_160GHz", "/a_3312368_578192_180GHz", "/a_3312368_397393_183GHz", "/a_3312368_582870_186GHz", "/a_3312368_578174_190GHz", "/a_3312368_578177_2GHz", ]; var selection = "/a_3312368_578189_120GHz"; var selectedFreq = getFreq(selection); function getFreq(s) { var parts = s.match(/(\\d+)(MHz|GHz)$/); return parts[1]* (parts[2] == "GHz" ? 1000: 1); } var string_array = arr.filter(function(el) { var elFreq = getFreq(el); return selectedFreq > elFreq; }); document.getElementById('r').innerHTML = JSON.stringify(string_array, null, 2); 

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