Quickest way to find position of item less than or equal to double in sorted list C# -


i exploring fastest way iterate through 3 sorted lists find position of first item equal or less double value. lists contains 2 columns of doubles.

i have 2 following working examples attached below, these encompassed bigger while loop (which modifies currentpressure list changing [0] value) value. but, considering amount of rows (500,000+) being parsed bigger while loop, code below slow (one iteration of 3 while loops takes >20 ms).

"allpressures" contains rows while currentpressure modified remaining code. while loops used align time flow, rpm , position lists time in pressure list.

in other words trying find quickest way determine x of instance 

flowlist[x].time =< currentpressure[0].time

any suggestions appreciated!

examples:

           (int = 0; < allpressures.count; i++)             {                 if (flowlist[i].time >= currentpressure[0].time)                 {                     fl = i;                     break;                 }             }              (int = 0; < allpressures.count; i++)             {                 if (rpmlist[i].time >= currentpressure[0].time)                 {                     rp = i;                     break;                 }             }              (int = 0; < allpressures.count; i++)             {                 if (positionlist[i].time >= currentpressure[0].time)                 {                     bp = i;                     break;                 }             }

using while loop:

            while (flowlist[fl].time < currentpressure[0].time)             {                 fl++;             }              while (rpmlist[rp].time < currentpressure[0].time)             {                 rp++;             }              while (positionlist[bp].time < currentpressure[0].time)             {                 bp++;             }

the problem doing linear search. means in worst case scenario iterating on elements in lists. gives computational complexity of o(3*n) n length of lists , 3 number of lists searching.

since lists sorted can use faster binary search has complexity of o(log(n)) , in case o(3*log(n)).

luckily don't have implement yourself, because .net offers helper method list.binarysearch(). need 1 takes custom comparer, because want compare pressuredata objects.

since looking index of closest value that's less search value, you'll have use little trick: when binarysearch() doesn't find matching value returns index of next element larger search value. it's easy find previous element smaller search value.

here extension method implements this:

public static int findmaxindex<t>(     list<t> sortedlist, t inclusiveupperbound, icomparer<t> comparer = null) {     var index = sortedlist.binarysearch(inclusiveupperbound, comparer);      // max value found in list. return index.     if (index >= 0)         return index;      // max value not found , "~index" index of     // next value greater search value.     index = ~index;      // there values in list less search value.     // return index of closest one.     if (index > 0)         return index - 1;      // values in list greater search value.     return -1; }

test @ https://dotnetfiddle.net/klzsm5

use method comparer understands pressuredata objects:

var pdc = comparer<pressuredata>.create((x, y) => x.time.compareto(y.time)); var fl = flowlist.findmaxindex(currentpressure[0], pdc);

here working example: https://dotnetfiddle.net/dmgzsv


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

c# - Asp.net web api : redirect unauthorized requst to forbidden page -

im trying redirect unauthorized request forbidden page instead i'm getting forbidden page in response body , how can fix ? here's startup class : app.createperowincontext(storecontext.create); app.createperowincontext<applicationusermanager>(applicationusermanager.create); app.createperowincontext<applicationsigninmanager>(applicationsigninmanager.create); app.usecookieauthentication(new cookieauthenticationoptions { authenticationtype = defaultauthenticationtypes.applicationcookie, expiretimespan = timespan.fromdays(30), }); app.useexternalsignincookie(defaultauthenticationtypes.externalcookie); app.usetwofactorsignincookie(defaultauthenticationtypes.twofactorcookie, timespan.fromminutes(5)); app.usetwofactorrememberbrowsercookie(defaultauthenticationtypes.twofactorrememberbrowsercookie); the method im trying reach : [httpget] [authorize(roles = "admin")] public string getcurrentusername() { return userman...
Read more