I am working on a project that requires the manipulation of enormous matrices, specifically pyramidal summation for a copula calculation.  

In short, I need to keep track of a relatively small number of values (usually a value of 1, and in rare cases more than 1) in a sea of zeros in the matrix (multidimensional array).  

A sparse array allows the user to store a small number of values, and assume all undefined records to be a preset value.  Since it is not physically possibly to store all values in memory, I need to store only the few non-zero elements. This could be several million entries.

Speed is a huge priority, and I would also like to dynamically choose the number of variables in the class at runtime.

I currently work on a system that uses a binary search tree (b-tree) to store entries. Does anyone know of a better system?

What is the best way to create a sparse array in C++?

Do my tiles need to adhere to any particular specs?

I have a large image file which I&#39;d like to turn into a map with LeafletJS. I am going to be using the Python Imaging Library to cut it up into all the various tiles I need. 

However, I can&#39;t find any information about using custom maps in Leaflet. Do I provide Leaflet with the range of X,Y,Z info somehow? Do I give it the pixel size of each tile? Does it figure this out on its own?

To put my question into one concise question: What do I need to do in order to have image files that can double as map tiles with LeafletJS, and what, if anything, do I need to do in my front-end script? (beyond the obvious specifying of my custom URL)

Using custom map image tiles in LeafletJS?

    def map = [name:&quot;Gromit&quot;, likes:&quot;cheese&quot;, id:1234]

I would like to access map in such a way that I can get the key

something like the output should be

map.keys returns array of string. basically i just want to get the keys

output:

    name
    likes
    id

Get key in groovy maps

**How to apply force repulsion on map&#39;s labels so they find their right places automatically ?** 

----
##Bostock&#39; &quot;Let&#39;s Make a Map&quot;

Mike Bostock&#39;s [Let&#39;s Make a Map](http://bost.ocks.org/mike/map/) (screenshot below). By default, labels are put at the point&#39;s coordinates and polygons/multipolygons&#39;s `path.centroid(d)` + a simple left or right align, so they frequently enter in conflict.

![enter image description here][1]

##Handmade label placements
One improvement [I met](http://wwwpub.zih.tu-dresden.de/~rklammer/html/mapOfGermany.html) requires to add an human made `IF` fixes, and to add as many as needed, such :

    .attr(&quot;dy&quot;, function(d){ if(d.properties.name===&quot;Berlin&quot;) {return &quot;.9em&quot;} })

The whole become increasingly dirty as the number of labels to reajust increase  :

    //places&#39;s labels: point objects
    svg.selectAll(&quot;.place-label&quot;)
        .data(topojson.object(de, de.objects.places).geometries)
      .enter().append(&quot;text&quot;)
        .attr(&quot;class&quot;, &quot;place-label&quot;)
        .attr(&quot;transform&quot;, function(d) { return &quot;translate(&quot; + projection(d.coordinates) + &quot;)&quot;; })
        .attr(&quot;dy&quot;, &quot;.35em&quot;)
        .text(function(d) { if (d.properties.name!==&quot;Berlin&quot;&amp;&amp;d.properties.name!==&quot;Bremen&quot;){return d.properties.name;} })
        .attr(&quot;x&quot;, function(d) { return d.coordinates[0] &gt; -1 ? 6 : -6; })
        .style(&quot;text-anchor&quot;, function(d) { return d.coordinates[0] &gt; -1 ? &quot;start&quot; : &quot;end&quot;; });
    
    //districts&#39;s labels: polygons objects.
    svg.selectAll(&quot;.subunit-label&quot;)
        .data(topojson.object(de, de.objects.subunits).geometries)
      .enter().append(&quot;text&quot;)
        .attr(&quot;class&quot;, function(d) { return &quot;subunit-label &quot; + d.properties.name; })
        .attr(&quot;transform&quot;, function(d) { return &quot;translate(&quot; + path.centroid(d) + &quot;)&quot;; })
        .attr(&quot;dy&quot;, function(d){
		//handmade IF
    	 	if( d.properties.name===&quot;Sachsen&quot;||d.properties.name===&quot;Th&#252;ringen&quot;|| d.properties.name===&quot;Sachsen-Anhalt&quot;||d.properties.name===&quot;Rheinland-Pfalz&quot;)
    			{return &quot;.9em&quot;}
    		else if(d.properties.name===&quot;Brandenburg&quot;||d.properties.name===&quot;Hamburg&quot;)
    			{return &quot;1.5em&quot;}
    		else if(d.properties.name===&quot;Berlin&quot;||d.properties.name===&quot;Bremen&quot;)
    			{return &quot;-1em&quot;}else{return &quot;.35em&quot;}}
        )
        .text(function(d) { return d.properties.name; });

##Need for better solution
That&#39;s just not manageable for larger maps and sets of labels. **How to add force repulsions to these both classes: `.place-label` and `.subunit-label`?**


This issue is quite a brain storming as I haven&#39;t deadline on this, but I&#39;am quite curious about it. I was thinking about this question as a basic D3js implementation of Migurski/[Dymo.py](https://github.com/migurski/Dymo). Dymo.py&#39;s README.md documentation set a large set of objectives, from which to select the core needs and functions (20% of the work, 80% of the result). 

 1. **Initial placement:** Bostock give a good start with left/right positionning relative to the geopoint. 
 2. **Inter-labels repulsion:** different approach are possible, Lars &amp; Navarrc proposed one each,
 3. **Labels annihilation:** A label annihilation function when one label&#39;s overall repulsion is too intense, since squeezed between other labels, with the priority of annihilation being either random or based on a `population` data value, which we can get via NaturalEarth&#39;s .shp file.
 4. [Luxury] **Label-to-dots repulsion:** with fixed dots and mobile labels. But this is rather a luxury. 

I ignore if label repulsion will work across layers and classes of labels. But getting countries labels and cities labels not overlapping may be a luxury as well.

  [1]: http://i.stack.imgur.com/HUuli.png

D3js: Automatic labels placement to avoid overlaps? (force repulsion)

I&#39;m trying to program geocoding. I created API key, but when I add it into my website code I don&#39;t get anything, however when I don&#39;t use API everything works well.  When I&#39;m sending:

    https://maps.googleapis.com/maps/api/geocode/json?address=&quot;.$adres.&quot;&amp;key=KLUCZ_XXX
    
I get a response:

    Browser API keys cannot have referer restrictions when used with this API.
    
If I use:

    https://maps.googleapis.com/maps/api/geocode/json?address=&quot;.$adres&quot; 
    
The result is correct but the number of queries is limited per day.

Key constraint: referrals HTTP (Web) - set to the domain from which conjure inquiry. Interface Google Maps Geocoding API is turned on.

Does the API key has to be activated also somewhere else to work?


API key Browser API keys cannot have referer restrictions when used with this API

I have the fallowing code:

    map: function (events) {
	    var arrayOfLatLngs = [];
		var _this = this;

		// setup a marker group
		var markers = L.markerClusterGroup();

		events.forEach(function (event) {
		    // setup the bounds
			arrayOfLatLngs.push(event.location);

			// create the marker
			var marker = L.marker([event.location.lat, event.location.lng]);

			marker.bindPopup(View(event));

			// add marker
			markers.addLayer(marker);
		});

		// add the group to the map
		// for more see https://github.com/Leaflet/Leaflet.markercluster
		this.map.addLayer(markers);

		var bounds = new L.LatLngBounds(arrayOfLatLngs);
		this.map.fitBounds(bounds);
		this.map.invalidateSize();
    }

I initially call this function and it will add all `events` to the map with markers and clusters.

at some lather point i pass in some other events, the map will zoom in to the new events but the old ones are still on the map.

I&#39;ve tried `this.map.removeLayer(markers);` and some other stuff, but I can&#39;t get the old markers to disappear

Any ideas?

How to clear leaflet map of all markers and layers before adding new ones?

I am trying to create a choropleth map of the US that has the default color changed from gray to white.

I have records for 18 of 48 states and the code works to color by value, but for those states where I have no records the states are gray. I would like them to be white.

How do I change the color?

    library(maps)
    library(plyr)
    library(ggplot2)
    records1&lt;-read.csv(&#39;E:/My Documents/records_by_state.csv&#39;)
    records&lt;-data.frame(state=tolower(rownames(records1)), records1)
    head(records)
    all_states&lt;-map_data(&quot;state&quot;)
    head(all_states)
    record_map&lt;-merge(all_states, records, by.x=&quot;region&quot;, by.y=&quot;state.name&quot;)
    record_map&lt;-arrange(record_map, group, order)
    head(record_map)

    p&lt;- ggplot()

    p&lt;- p + geom_polygon(data=record_map, aes(x=long, y=lat, group=group,    fill=record_map$Records), colour=&quot;black&quot;
             )+ scale_fill_continuous(low=&quot;thistle2&quot;, high=&quot;darkred&quot;, guide=&quot;colorbar&quot;)
    P1 &lt;- p + theme_bw() +labs(fill= &quot;Records by State&quot;
                        , title= &quot;By State&quot;, x=&quot;&quot;, y=&quot;&quot;)
    P1 + scale_y_continuous(breaks=c()) + scale_x_continuous(breaks=c()) +  theme(panel.border= element_blank())





  [1]: http://i.stack.imgur.com/bdwkx.jpg

How do I change the NA color from gray to white in a ggplot choropleth map?

How do I calculate the distance between two points specified by latitude and longitude?

For clarification, I&#39;d like the distance in kilometers; the points use the WGS84 system and I&#39;d like to understand the relative accuracies of the approaches available.

Calculate distance between two latitude-longitude points? (Haversine formula)

I&#39;m trying to iterate over a typescript map but I keep getting errors and I could not find any solution yet for such a trivial problem.

My code is:

    myMap : Map&lt;string, boolean&gt;;
    for(let key of myMap.keys()) {
       console.log(key);
    }

And I get the Error:

&gt;Type &#39;IterableIteratorShim&lt;[string, boolean]&gt;&#39; is not an array type or a string type.

Full Stack Trace:

     Error: Typescript found the following errors:
      /home/project/tmp/broccoli_type_script_compiler-input_base_path-q4GtzHgb.tmp/0/src/app/project/project-data.service.ts (21, 20): Type &#39;IterableIteratorShim&lt;[string, boolean]&gt;&#39; is not an array type or a string type.
        at BroccoliTypeScriptCompiler._doIncrementalBuild (/home/project/node_modules/angular-cli/lib/broccoli/broccoli-typescript.js:115:19)
        at BroccoliTypeScriptCompiler.build (/home/project/node_modules/angular-cli/lib/broccoli/broccoli-typescript.js:43:10)
        at /home/project/node_modules/broccoli-caching-writer/index.js:152:21
        at lib$rsvp$$internal$$tryCatch (/home/project/node_modules/rsvp/dist/rsvp.js:1036:16)
        at lib$rsvp$$internal$$invokeCallback (/home/project/node_modules/rsvp/dist/rsvp.js:1048:17)
        at lib$rsvp$$internal$$publish (/home/project/node_modules/rsvp/dist/rsvp.js:1019:11)
        at lib$rsvp$asap$$flush (/home/project/node_modules/rsvp/dist/rsvp.js:1198:9)
        at _combinedTickCallback (internal/process/next_tick.js:67:7)
        at process._tickCallback (internal/process/next_tick.js:98:9)

I&#39;m using angular-cli beta5 and typescript 1.8.10 and my target is es5.
Has anyone had this Problem?

Iterating over Typescript Map

The following code says that passing the map as `const` into the `operator[]` method discards qualifiers:

    #include &lt;iostream&gt;
    #include &lt;map&gt;
    #include &lt;string&gt;
    
    using namespace std;
    
    class MapWrapper {
    public:
        const int &amp;get_value(const int &amp;key) const {
            return _map[key];
        }
    
    private:
        map&lt;int, int&gt; _map;
    };
    
    int main() {
        MapWrapper mw;
        cout &lt;&lt; mw.get_value(42) &lt;&lt; endl;
        return 0;
    }

Is this because of the possible allocation that occurs on the map access? Can no functions with map accesses be declared const?

    MapWrapper.cpp:10: error: passing const std::map&lt;int, int, std::less&lt;int&gt;,
    std::allocator&lt;std::pair&lt;const int, int&gt; &gt; &gt; as this argument of 
    _Tp&amp; std::map&lt;_Key, _Tp, _Compare, _Alloc&gt;::operator[](const _Key&amp;) 
    [with _Key = int, _Tp = int, _Compare = std::less&lt;int&gt;, 
    _Alloc = std::allocator&lt;std::pair&lt;const int, int&gt; &gt;] discards qualifiers

C++ map access discards qualifiers (const)

I am building a map application using Angular Maps and want to import a JSON file as a list of markers defining locations. I&#39;m hoping to use this JSON file as marker[] array inside the app.component.ts . Instead of defining a hardcoded array of markers inside the TypeScript file.

What is the best process of importing this JSON file for use in my project? Any direction greatly appreciated!

How to import JSON File into a TypeScript file?

The issue here is not exactly how to plot maps through R, as I have found already a pretty nice example [here][1], but rather how to make it work. In fact, I am unable to load library `rgdal`:

    library(rgdal)
    Error in library(rgdal) : there is no package called ‘rgdal’

However, when I try to install the above package manually, I get the following error:

    ....
    configure: error: proj_api.h not found in standard or given locations.
    ERROR: configuration failed for package ‘rgdal’
    * removing ‘/home/eualin/R/i686-pc-linux-gnu-library/2.15/rgdal’
    Warning in install.packages : installation of package ‘/home/eualin/Downloads/rgdal_0.8-5.tar.gz’ had non-zero exit status

Any input welcome!

  [1]: http://rpsychologist.com/parsing-data-from-a-text-file-and-plotting-where-people-live-using-ggplot2-and-openstreetmaps/

rgdal package installation

Is there a way to embed/mashup the OpenStreetMap in your page (like the way [Google Maps API][1] works)?

I need to show a map inside my page with some markers and allow dragging/zooming around, maybe routing.
I suspect there would be some Javascript API for this, but I can&#39;t seem to find it.

Searching gets me an [API for access to raw map data][2], but that seems to be more for map editing; besides, working with that would be a heavy task for AJAX.


  [1]: http://code.google.com/apis/maps/
  [2]: http://wiki.openstreetmap.org/wiki/API

Openstreetmap: embedding map in webpage (like Google Maps)

I want to make an app which checks the nearest place where a user is. I can easily get the location of the user and I have already a list of places with latitude and longitude.

What would be the best way to know the nearest place of the list against the current user location. 

I could not find anything in the google APIs.  



Get the distance between two geo points

I have a table-driven test case like this one:

    func CountWords(s string) map[string]int

    func TestCountWords(t *testing.T) {
      var tests = []struct {
        input string
        want map[string]int
      }{
        {&quot;foo&quot;, map[string]int{&quot;foo&quot;:1}},
        {&quot;foo bar foo&quot;, map[string]int{&quot;foo&quot;:2,&quot;bar&quot;:1}},
      }
      for i, c := range tests {
        got := CountWords(c.input)
        // TODO test whether c.want == got
      }
    }

I could check whether the lengths are the same and write a loop that checks if every key-value pair is the same. But then I have to write this check again when I want to use it for another type of map (say `map[string]string`).

What I ended up doing is, I converted the maps to strings and compared the strings:

    func checkAsStrings(a,b interface{}) bool {
      return fmt.Sprintf(&quot;%v&quot;, a) != fmt.Sprintf(&quot;%v&quot;, b) 
    }

    //...
    if checkAsStrings(got, c.want) {
      t.Errorf(&quot;Case #%v: Wanted: %v, got: %v&quot;, i, c.want, got)
    }

This assumes that the string representations of equivalent maps are the same, which seems to be true in this case (if the keys are the same then they hash to the same value, so their orders will be the same). Is there a better way to do this? What is the idiomatic way to compare two maps in table-driven tests?

How to test the equivalence of maps in Golang?

Bearing in mind that I&#39;ll be performing calculations on lat / long pairs, what datatype is best suited for use with a MySQL database?


What is the ideal data type to use when storing latitude / longitude in a MySQL database?

Is there a way I can dynamically add data to a map in javascript. A `map.put(key,value)`? I am using the yui libraries for javascript, but didn&#39;t see anything there to support this. 



Dynamically add data to a javascript map

How can I merge two STL maps into one? They both have the same key and value types (`map&lt;string, string&gt;`). If there is an overlap of the keys, I would like to give preference to one of the maps.

How can I merge two STL maps?

I can&#39;t find an example on how to intercept the map touch on the new Google Maps API v2.

I need to know when the user touches the map in order to stop a thread (the centering of the map around my current location).


Google Maps Android API v2 - detect touch on map

The code below is creating a new map called `nameTable`, then adding an entry named example to it, then trying to print the name property of the Value.

When I run it, it seems that the plus operation didn&#39;t add a new entry to the map like I thought it would.

So what am I doing wrong? 

    class Person(name1: String, lastName1: String, age1: Int){
        var name: String = name1
        var lastName: String = lastName1
        var age: Int = age1
    }

    var nameTable: MutableMap&lt;String, Person&gt; = mutableMapOf()
    var example = Person(&quot;Josh&quot;, &quot;Cohen&quot;, 24)

    fun main (args: Array&lt;String&gt;){
        nameTable.plus(Pair(&quot;person1&quot;, example))
        for(entry in nameTable){
            println(entry.value.age)
        }
    }

While we&#39;re at it, I would love some examples of how to add, remove, and get an entry from a map.

How to work with Maps in Kotlin

I&#39;m trying to convert a lat/long point into a 2d point so that I can display it on an image of the world-which is a mercator projection.

I&#39;ve seen various ways of doing this and a few questions on stack overflow-I&#39;ve tried out the different code snippets and although I get the correct longitude to pixel, the latitude is always off-seems to be getting more reasonable though.

I need the formula to take into account the image size, width etc. 

I&#39;ve tried this piece of code:

    double minLat = -85.05112878;
    double minLong = -180;
    double maxLat = 85.05112878;
    double maxLong = 180;

    // Map image size (in points)
    double mapHeight = 768.0;
    double mapWidth = 991.0;

    // Determine the map scale (points per degree)
    double xScale = mapWidth/ (maxLong - minLong);
    double yScale = mapHeight / (maxLat - minLat);
    
    // position of map image for point
    double x = (lon - minLong) * xScale;
    double y = - (lat + minLat) * yScale;

    System.out.println(&quot;final coords: &quot; + x + &quot; &quot; + y);


The latitude seems to be off by about 30px in the example I&#39;m trying. Any help or advice?

*Update*

Based on this question:[Lat/lon to xy][1]

I&#39;ve tried to use the code provided but I&#39;m still having some problems with latitude conversion, longitude is fine.

    int mapWidth = 991;
    int mapHeight = 768;

    double mapLonLeft = -180;
    double mapLonRight = 180;
    double mapLonDelta = mapLonRight - mapLonLeft;

    double mapLatBottom = -85.05112878;
    double mapLatBottomDegree = mapLatBottom * Math.PI / 180;
    double worldMapWidth = ((mapWidth / mapLonDelta) * 360) / (2 * Math.PI);
    double mapOffsetY = (worldMapWidth / 2 * Math.log((1 + Math.sin(mapLatBottomDegree)) / (1 - Math.sin(mapLatBottomDegree))));

    double x = (lon - mapLonLeft) * (mapWidth / mapLonDelta);
    double y = 0.1;
    if (lat &lt; 0) {
        lat = lat * Math.PI / 180;
        y = mapHeight - ((worldMapWidth / 2 * Math.log((1 + Math.sin(lat)) / (1 - Math.sin(lat)))) - mapOffsetY);
    } else if (lat &gt; 0) {
        lat = lat * Math.PI / 180;
        lat = lat * -1;
        y = mapHeight - ((worldMapWidth / 2 * Math.log((1 + Math.sin(lat)) / (1 - Math.sin(lat)))) - mapOffsetY);
        System.out.println(&quot;y before minus: &quot; + y);
        y = mapHeight - y;
    } else {
        y = mapHeight / 2;
    }
    System.out.println(x);
    System.out.println(y);

When using the original code if the latitude value is positive it returned a negative point, so I modified it slightly and tested with the extreme latitudes-which should be point 0 and point  766, it works fine. However when I try a different latitude value ex: 58.07 (just north of the UK) it displays as north of Spain. 


  [1]: https://stackoverflow.com/questions/2103924/mercator-longitude-and-latitude-calculations-to-x-and-y-on-a-cropped-map-of-the/10401734#10401734


Convert latitude/longitude point to a pixels (x,y) on mercator projection

How to move a particular HashMap entry to Last position?

For Example, I have HashMap values like this:

    HashMap&lt;String,Integer&gt; map = new HashMap&lt;String,Integer&gt;();
    
    map= {Not-Specified 1, test 2, testtest 3};

&quot;Not-Specified&quot; may come in any position. it may come first or in the middle of the map. But i want to move the &quot;Not-Specified&quot; to the last position.

How can I do that? thanks in advance.

Accessing the last entry in a Map

I want to be able to get a estimate of the distance between two (latitude, longitude) points. I want to undershoot, as this will be for A* graph search and I want it to be **fast**. The points will be at most 800 km apart.

How can I quickly estimate the distance between two (latitude, longitude) points?

I am trying to open google maps or maps in my `react-native` application.

When I run the app on my iPhone/simulator, I receive this error
```
&quot;Don&#39;t know how to open URI:...&quot;.
```

What I am doing wrong?

My code:
```javascript
    openGps() {
      var url = &#39;geo:37.484847,-122.148386&#39;
      this.openExternalApp(url)
    }
    
    openExternalApp(url) {
      Linking.canOpenURL(url).then(supported =&gt; {
        if (supported) {
          Linking.openURL(url);
        } else {
          console.log(&#39;Don\&#39;t know how to open URI: &#39; + url);
        }
      });
    }
```

open maps/google maps in react native

i need to know long and lat of my four corners of current area
as in this image

![enter image description here][1]

i have tried this but with no luck :

    map.getBounds();

any help ?
  [1]: http://i.stack.imgur.com/cqb1T.png

All Maps Solutions on Gang of Coders

Total of 25 Maps Solutions