Merge pull request #22 from gleam-community/list-at-hotfix

`list.at` hotfix

gleam.toml

@@ -1,5 +1,5 @@
 name = "gleam_community_maths"
-version = "1.1.0"
+version = "1.1.1"
 
 licences = ["Apache-2.0"]
 description = "A basic maths library"
@@ -7,7 +7,7 @@ repository = { type = "github", user = "gleam-community", repo = "maths" }
 gleam = ">= 0.32.0"
 
 [dependencies]
-gleam_stdlib = "~> 0.34"
+gleam_stdlib = "~> 0.38"
 
 [dev-dependencies]
 gleeunit = "~> 1.0"

manifest.toml

@@ -2,10 +2,10 @@
 # You typically do not need to edit this file
 
 packages = [
-  { name = "gleam_stdlib", version = "0.36.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "C0D14D807FEC6F8A08A7C9EF8DFDE6AE5C10E40E21325B2B29365965D82EB3D4" },
+  { name = "gleam_stdlib", version = "0.38.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "663CF11861179AF415A625307447775C09404E752FF99A24E2057C835319F1BE" },
   { name = "gleeunit", version = "1.1.2", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "72CDC3D3F719478F26C4E2C5FED3E657AC81EC14A47D2D2DEBB8693CA3220C3B" },
 ]
 
 [requirements]
-gleam_stdlib = { version = "~> 0.34" }
+gleam_stdlib = { version = "~> 0.38" }
 gleeunit = { version = "~> 1.0" }

src/gleam_community/maths/metrics.gleam

@@ -48,13 +48,13 @@
 ////   * [`standard_deviation`](#standard_deviation)
 ////
 
-import gleam_community/maths/elementary
-import gleam_community/maths/piecewise
-import gleam_community/maths/arithmetics
-import gleam_community/maths/predicates
-import gleam_community/maths/conversion
+import gleam/bool
 import gleam/list
 import gleam/pair
+import gleam_community/maths/arithmetics
+import gleam_community/maths/conversion
+import gleam_community/maths/elementary
+import gleam_community/maths/piecewise
 import gleam/set
 import gleam/float
 import gleam/int
@@ -593,33 +593,31 @@ pub fn mean(arr: List(Float)) -> Result(Float, String) {
 ///     </a>
 /// </div>
 ///
-pub fn median(arr: List(Float)) -> Result(Float, String) {
-  case arr {
-    [] ->
-      "Invalid input argument: The list is empty."
-      |> Error
-    _ -> {
-      let count: Int = list.length(arr)
-      let mid: Int = list.length(arr) / 2
-      let sorted: List(Float) = list.sort(arr, float.compare)
-      case predicates.is_odd(count) {
-        // If there is an odd number of elements in the list, then the median
-        // is just the middle value
-        True -> {
-          let assert Ok(val0) = list.at(sorted, mid)
-          val0
-          |> Ok
-        }
-        // If there is an even number of elements in the list, then the median
-        // is the mean of the two middle values
-        False -> {
-          let assert Ok(val0) = list.at(sorted, mid - 1)
-          let assert Ok(val1) = list.at(sorted, mid)
-          [val0, val1]
-          |> mean()
-        }
-      }
+pub fn median(arr: List(Float)) -> Result(Float, Nil) {
+  use <- bool.guard(list.is_empty(arr), Error(Nil))
+  let length = list.length(arr)
+  let mid = length / 2
+
+  case length % 2 == 0 {
+    True -> do_median(arr, mid, True, 0)
+    False -> do_median(arr, mid, False, 0)
   }
+}
+
+fn do_median(
+  xs: List(Float),
+  mid: Int,
+  mean: Bool,
+  index: Int,
+) -> Result(Float, Nil) {
+  use <- bool.guard(index > mid, Error(Nil))
+  let mid_less_one = mid - 1
+
+  case xs {
+    [x, ..] if !mean && index == mid -> Ok(x)
+    [x, y, ..] if mean && index == mid_less_one -> Ok({ x +. y } /. 2.0)
+    [_, ..rest] -> do_median(rest, mid, mean, index + 1)
+    [] -> Error(Nil)
   }
 }
 

src/gleam_community/maths/piecewise.gleam

@@ -52,11 +52,11 @@
 ////   * [`arg_maximum`](#arg_maximum)
 ////
 
-import gleam/option
+import gleam/int
 import gleam/list
+import gleam/option
 import gleam/order
 import gleam/pair
-import gleam/int
 import gleam_community/maths/conversion
 import gleam_community/maths/elementary
 
@@ -944,17 +944,15 @@ pub fn list_minimum(
     [] ->
       "Invalid input argument: The list is empty."
       |> Error
-    _ -> {
-      let assert Ok(val0) = list.at(arr, 0)
-      arr
-      |> list.fold(val0, fn(acc: a, element: a) {
+    [x, ..rest] ->
+      Ok(
+        list.fold(rest, x, fn(acc: a, element: a) {
           case compare(element, acc) {
             order.Lt -> element
             _ -> acc
           }
-      })
-      |> Ok
-    }
+        }),
+      )
   }
 }
 
@@ -1000,17 +998,15 @@ pub fn list_maximum(
     [] ->
       "Invalid input argument: The list is empty."
       |> Error
-    _ -> {
-      let assert Ok(val0) = list.at(arr, 0)
-      arr
-      |> list.fold(val0, fn(acc: a, element: a) {
+    [x, ..rest] ->
+      Ok(
+        list.fold(rest, x, fn(acc: a, element: a) {
           case compare(acc, element) {
             order.Lt -> element
             _ -> acc
           }
-      })
-      |> Ok
-    }
+        }),
+      )
   }
 }
 
@@ -1202,11 +1198,9 @@ pub fn extrema(
     [] ->
       "Invalid input argument: The list is empty."
       |> Error
-    _ -> {
-      let assert Ok(val_max) = list.at(arr, 0)
-      let assert Ok(val_min) = list.at(arr, 0)
-      arr
-      |> list.fold(#(val_min, val_max), fn(acc: #(a, a), element: a) {
+    [x, ..rest] ->
+      Ok(
+        list.fold(rest, #(x, x), fn(acc: #(a, a), element: a) {
           let first: a = pair.first(acc)
           let second: a = pair.second(acc)
           case compare(element, first), compare(second, element) {
@@ -1215,8 +1209,7 @@ pub fn extrema(
             _, order.Lt -> #(first, element)
             _, _ -> #(first, second)
           }
-      })
-      |> Ok
-    }
+        }),
+      )
   }
 }