Simple count of unique items in javascript array -


looking count of unique filenames contained in simple javascript array.

i have javascript array combines 2 arrays via 

var total_dl = prev_dl.concat(new_dl).sort();

one json_encode() php variable, other made checkbox values selected on form. outputs simple list of file names, ie 

    cat.jpg, dog.jpg, elephant.jpg, cat.jpg, lion.jpg, dog.jpg

i can refine array of distinct values, 

var unique_dl = total_dl.filter((value,pos) => {return total_dl.indexof(value) == pos;} );

to output 

    cat.jpg, dog.jpg, elephant.jpg, lion.jpg

i need output count of how many unique/distinct filenames contained here, ie 4. first thought use length 

var count_unique = unique_dl.length;

which seems give value of prev_dl + 1, unchanged whatever new_dl made of. try with

var count_unique = unique_dl.filter(function(val, i, arr) {      return arr.indexof(val) === i; }).length;

fails (have misformatted here?).

any pointers/steers here welcome, thanks.

the unique_dl.length solution works me. building unique_dl thou needs o(n^2) time, it's slower than:

function count_unique(in_array) {     if(in_array.length == 0)         return 0;     var sorted = input_array.sort();     var unique_count = 1;     for(int = 1; < sorted.length; ++i)         if(sorted[i - 1] != sorted[i])             ++unique_count;     return unique_count;  }

since uses o(n log(n)) time


Comments

Post a Comment

Popular posts from this blog

Is there a better way to structure post methods in Class Based Views -

i'm using class based views in django , never specify url in ajax calls , omit action parameter in form because know these requests go through post method of class based view. notice view - profile page make many requests depending on user updating on page - post method become convoluted , if/else mess example: def post(self, request, *args, **kwargs): # handle user changing available date if request.post.get('availabledate') != none: self.updateavailabledate(request) return jsonresponse({'result':'success'}) if request.post.get('newprojectname') != none: creative_user = creativeuserprofile.objects.get(id = request.user.id) project = project.create_project(creative_user, request.post['newprojectname']) project.save() return jsonresponse({'projectid': project.id }) if request.post.get('projectimage') != none , request.files['file']: proj
Read more

performance - Why is XCHG reg, reg a 3 micro-op instruction on modern Intel architectures? -

i'm doing micro-optimization on performance critical part of code , came across sequence of instructions (in at&t syntax): add %rax, %rbx mov %rdx, %rax mov %rbx, %rdx i thought had use case xchg allow me shave instruction , write: add %rbx, %rax xchg %rax, %rdx however, dimay found agner fog's instruction tables , xchg 3 micro-op instruction 2 cycle latency on sandy bridge, ivy bridge, broadwell, haswell , skylake. 3 whole micro-ops , 2 cycles of latency! 3 micro-ops throws off 4-1-1-1 cadence , 2 cycle latency makes worse original in best case since last 2 instructions in original might execute in parallel. now... cpu might breaking instruction micro-ops equivalent to: mov %rax, %tmp mov %rdx, %rax mov %tmp, %rdx where tmp anonymous internal register , suppose last 2 micro-ops run in parallel latency 2 cycles. given register renaming occurs on these micro-architectures, though, doesn't make sense me done way. why wouldn't register renamer
Read more

jquery - Responsive Navbar with Sub Navbar -

good day, forgive me nav vocabulary not best. if question confusing apologize. i'm working on navigation bar needs centered on page @ 768px , above. items in nav open (or perhaps toggle) subnav lives directly below. these nav should appear centered on page. i have been able work through responsive portion of nav bar, having main items align vertically , sub nav menu of each item roll out below, , gave them indent separation. working well. however, issue not responsive side, behavior @ width greater 768px. happens toggling menu's sub navigation pushes other main items down page below sub nav. here's code: $(document).ready(function () { //stick in fixed 100% height behind navbar don't wrap $('#slide-nav.navbar-inverse').after($('<div class="inverse" id="navbar-height-col"></div>')); $('#slide-nav.navbar-default').after($('<div id="navbar-height-col"></d
Read more