do loops on singletons (#256)

* do loops on singletons

* Update fixedeffects.jl

* Update fit.jl

* Update fit.jl

* Update fit.jl

* Update Project.toml

* Update fit.jl

* Update fit.jl

Author: matthieugomez

Project.toml

@@ -1,6 +1,6 @@
 name = "FixedEffectModels"
 uuid = "9d5cd8c9-2029-5cab-9928-427838db53e3"
-version = "1.10.1"
+version = "1.10.2"
 
 [deps]
 DataFrames = "a93c6f00-e57d-5684-b7b6-d8193f3e46c0"

src/fit.jl

@@ -154,11 +154,13 @@ function StatsAPI.fit(::Type{FixedEffectModel},
     esample .&= Vcov.completecases(df, vcov)
     fes, ids, fekeys, formula = parse_fixedeffect(df, formula)
     has_fes = !isempty(fes)
-    if has_fes
-        if drop_singletons
-            for fe in fes
-                drop_singletons!(esample, fe)
-            end
+    #TODO: add tests + return n_singletons
+    n_singletons = 0
+    while has_fes && drop_singletons
+        ns = Tuple(drop_singletons!(esample, fe) for fe in fes)
+        n_singletons += sum(ns)
+        if sum(ns) == first(ns)
+            break
         end
     end
     save_fe = (save == :fe) | ((save == :all) & has_fes)

src/utils/fixedeffects.jl

@@ -5,17 +5,20 @@
 ##############################################################################
 
 function drop_singletons!(esample, fe::FixedEffect)
+    n = 0
     cache = zeros(Int, fe.n)
     @inbounds for i in eachindex(esample)
         if esample[i]
             cache[fe.refs[i]] += 1
         end
     end
     @inbounds for i in eachindex(esample)
-        if esample[i]
-            esample[i] = cache[fe.refs[i]] > 1
+        if esample[i] && (cache[fe.refs[i]] == 1)
+            esample[i] = false
+            n += 1
         end
     end
+    return n
 end
 
 ##############################################################################
@@ -51,4 +54,4 @@ function isnested(fe::FixedEffect, prefs)
         end
     end
     return true
-end
+end