c# - How to do a loop to sort and update list<> based on specific condition -

i have list of 3d data inside list namely c_top

the c_top list consist of pattern orders y value in descending order , below:

//[ x,  y, z]         [ 2, 10, 1] //c_top[0]   [ 7,  8, 1] //c_top[1]   [ 1,  7, 2] //c_top[2]   [ 3,  6, 1] //c_top[3]   [ 4,  6, 2] //c_top[4]   .               .      .               .    .           //c_top[ctop.count - 1] 

now, objective x value inside c_top list based on condition has same z value

for (int = 0; < c_top.count; i++) {     if (i != c_top.count - 1)     {         // if next data , current data has same z, proceed         if (c_top[i].p.z == c_top[i + 1].p.z)         {             // if x of next data greater current x of current data             if (c_top[i + 1].p.x > c_top[i].p.x)             {                 // select x , y value @ x+ direction                 xy_xpluslist = c_top.select(x => x.p.x).orderby(x => x).tolist();             }              // if x of next data smaller current x of current data             else if (c_top[i + 1].p.x < c_top[i].p.x)             {                 // select x , y value @ x- direction                 xy_xminuslist = c_top.select(x => x.p.x).orderbydescending(x => x).tolist();             }         }          if (xy_xpluslist.count > 0)         {               //do         }          if (xy_xminuslist.count > 0)         {               //do         } } 

i using above loop, , above data example. due reason of c_top[1] , c_top[2] has different value of z. therefore, when i = 1, the c_top[1].p.x not saved has same z in c_top[0]

i result this

//output xy_xpluslist  =  { 2 } //only 1 x values  c_top[0] saved xy_xminuslist =  { 0 } 

but result want when

c_top[0] // output xy_xpluslist = { 2, 3 }           //       xy_xminuslist = { 0 }  c_top[1] // output xy_xpluslist = { 0 }          //       xy_xminuslist = { 3 }  c_top[2] // output xy_xpluslist  = { 1 , 4 }          //        xy_xminuslist = { 0 }  c_top[3] // ouput xy_xpluslist  = { 7 }          //       xy_xminuslist = { 2 }  c_top[4] // ouput xy_xpluslist  = { 0 }          //       xy_xminuslist = { 1 } 

in short. want consider each of data inside c_top list.

when considering c_top[i]:

if of data of z value inside c_top list has same z c_top[i].p.z, check x value inside c_top list.

if got x value greater c_top[i].p.x, x added xy_xpluslist

if got x value smaller c_top[i].p.x, x added xy_minuslist

is there linq way on doing it?

something after sort same z, check x inside list, , add xy_xpluslist

explanation update

in each of coordinate in list, first check @ same z field or not. if same z field, check x.

if x greater current x coordinate, add x xpluslist

if x smaller current x coordinate, add x xminuslist

*i repeat above process of coordinate inside list.

explanation update2

imaging tip of pyramid polygon above 1 coordinate in c_top list

to draw pyramid polygon, need coordinate of tip, coordinate of rhs tip , coordinate of lhs tip, coordinate of front, , coordinate back.

so, now, question. have stored multiple tip coordinate inside c_top list. want check coordinates in rhs tip (in +x direction) , lhs tip (in -x direction). , same front , coordinates.

imaging have multiple tip coordinate arranged in same z field different height. want connected of tip respect highest tip coordinate show pink color line below:

update: answer question myself , question shall closed

//group z coordinate throughout v_tip list var groupedz = p in v_tip                group p p.p.z q                select q;  foreach (var groupz in groupedz) {     //order groupz y coordinate descending order     var samezlist = groupz.orderbydescending(y => y.p.y).thenby(x => x.p.x).tolist();      //since list order descending w.r.t y coordinate, samezlist[0] peak coordinate in groupz     var peakz = samezlist[0];      // @ same z, mean @ xy plane     (int = 1; < samezlist.count; i++)     {         // mean x @ rhs peak         if (peakz.p.x < samezlist[i].p.x)         {             // add x , y coordinates in rhs direction peak (x+ direction peak             xy_xpluslist.add(samezlist[i].p.x);             xy_ypluslist.add(samezlist[i].p.y);         }         else // x @ lhs peak         {             // add x , y coordinates in lhs direction peak (x- direction peak             xy_xminuslist.add(samezlist[i].p.x);             xy_yminuslist.add(samezlist[i].p.y);         }     }  } 

i'm not sure i'm 100% on question... how's work you?

    public void dowork(list<int[]> c_top)     {         var distinctzvalues = c_top.select(p => p[2]); // gets enumerable object of unique z values          list<int[]> xy_minus = new list<int[]>();         list<int[]> xy_plus = new list<int[]>();          foreach (var z in distinctzvalues)         {             list<int[]> coords = c_top.where(p => p[2] == z).tolist(); // pull int[] c_top z == z             foreach (int[] coord in coords)                 if (coord[0] > coord[1])                     xy_minus.add(coord);                 else                     xy_plus.add(coord);         }     } 

or, after further review, might looking unique lists based on z value...

public void dowork2(list<int[]> c_top)     {         var distinctzvalues = c_top.select(p => p[2]); // gets enumerable object of unique z values          dictionary<int, list<int[]>> xy_minus = new dictionary<int, list<int[]>>();         dictionary<int, list<int[]>> xy_plus = new dictionary<int, list<int[]>>();          foreach (var z in distinctzvalues)         {             list<int[]> minus = new list<int[]>();             list<int[]> plus = new list<int[]>();             list<int[]> coords = c_top.where(p => p[2] == z).tolist(); // pull int[] c_top z == z             foreach (int[] coord in coords)                 if (coord[0] > coord[1])                     minus.add(coord);                 else                     plus.add(coord);             xy_minus.add(z, minus);             xy_plus.add(z, plus);         }     }