length of Array not stable

so i have a controller where i call a service that gets me items from the data base, I store these items in an Array then i use this array in another function, only when i do so the length of the array changes so my loop starts over everytime i'm still quite confused when it comes to the behavior of the callbacks and i think this is the reason behind this problem, here is my code :

my service :

//get a task by id 
            getTachebyId : function(id_Data){
                 return $http.get('/api/taches/' + id_Data);
            },

The controller :

 //Récupérer les enregistrements de la feuille de temps : 
          FT.getFT().then(function (result) {
                for(var i=0; i<result.data.ftListe.length;i++)
                {
                 //Récupérer le collaborateur : 
                     Compte.getComptesbyId(result.data.ftListe[i].collaborateurid).then(function(result)
                       {

                          lecollaborateur.push(result.data.col);

                       }); 
                  // Récupérer les taches remplie dans la feuille de temps et le projet équivalent 
                   Tache.getTachebyId(result.data.ftListe[i].tacheid).then(function(result)
                       {
                           task.push(result.data.tachelistes);
                        }); 


                  }
                 $scope.ftListe = result.data.ftListe;
                 $scope.task = task;
                 $scope.lecollaborateur = lecollaborateur;
                 //$scope.projets = projets;
            });
  //my function where I use the task array : 
    $scope.calculTotal= function(id)
       {
         var couttotal=0; 
         var count =0;
         console.log(task.length);
         for (var j=0;j<task.length;j++)
                  {
                     if(task[j].projet_id==id)
                      { //code }
                  }
    };

result of console.log(task.length) :

How can I get directly length = 5 ?

via jihane