在一个数组中查找比另一个数组大的元素

Question

There are 2 arrays data1 and data2 . The desired result is an array containing all the elements in data1 which are larger than the largest element in data2 [+ the 3 before as defined in variable buffer ]. In other words, the result should also include the previous 3 elements in data1 preceding the matched elements. Both arrays are already sorted in ascending order.

My code below does what is required, but is there a better way to do the same thing? Will regex be faster?

Data set

data1 = [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]
data2 = [102, 104, 106, 108]
buffer = 3

The desired result is [106, 107, 108, 109, 110]

Algorithm

largestData2 = _.max(data2)
data1LargerThanData2 = _.filter(data1, function(data1) {
    return data1 > largestData2
})
smallestData1LargerThanData2 = _.min(data1LargerThanData2)

sliceStart = data1.indexOf(smallestData1LargerThanData2) - buffer
result = data1.slice(sliceStart)

Answer 1

JSFIDDLE DEMO

var data1 = [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110],
data2 = [102, 104, 106, 108];
var maxData2 = Math.max.apply(Math, data2);

var newData = [];
data1.map(function(val) {
    if(val > maxData2) {
        newData.push(val);
    }
});
var index = data1.indexOf(newData[0]); //getting index of 1st element

var prev3Arr = [data1[index-3], data1[index-2], data1[index-1]]; //forming prev 3 elements

var finalResult = $.merge( prev3Arr, newData); // merging both arrays

console.log(finalResult);

Check your console for result: [106, 107, 108, 109, 110]

Answer 2

Start by getting the largest value in data2 :

var max = Math.max.apply(null, data2);

Then get all of the numbers from data1 that are greater than max :

var arr = data1.filter(function (el) {
  return el > max;
});

Use value of the first value in arr to find our starting point in data1 and take the appropriate chunk of elements from it.

var index = data1.indexOf(arr[0]) - 3;
var chunk = data1.slice(index, index + 3);

Merge arr into chunk .

chunk.push.apply(chunk, arr); // chunk = [106, 107, 108, 109, 110]

Demo .

Answer 3

Assuming the arrays are always in order:

var result;
var largestData2 = data2.slice( -1 );

_.each( data1, function( x, index ){
    if( x  > largestData2 ){
        result = data1.slice( index - buffer - 1 );
        return false;
    }
} );

Answer 4

If the two arrays are sorted ascending, you can omit max and just pick the last element

var largestData2 = data2[data2.length - 1];

To find the position in data1 being larger than largest_data2 , you can use a binary search and then go back three elements

var smallestData1LargerThanData2Index = binarySearch(data1, largestData2);
var sliceStart = smallestData1LargerThanData2Index - buffer;
if (sliceStart < 0)
    sliceStart = 0;

var result = data1.slice(sliceStart);

JSFiddle

Update:

Updated JSFiddle to actually use underscore.js .

Answer 5

You want all the values from data1 that are larger than the largest value of data2? If so How might I find the largest number contained in a JavaScript array? this might help