Add strain (#794)

config.json

@@ -525,6 +525,14 @@
           "math"
         ]
       },
+      {
+        "slug": "strain",
+        "name": "Strain",
+        "uuid": "b16f98d5-60af-4f03-922a-ff2a98fd5c2b",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "protein-translation",
         "name": "Protein Translation",

exercises/practice/strain/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Implement the `keep` and `discard` operation on collections.
+Given a collection and a predicate on the collection's elements, `keep` returns a new collection containing those elements where the predicate is true, while `discard` returns a new collection containing those elements where the predicate is false.
+
+For example, given the collection of numbers:
+
+- 1, 2, 3, 4, 5
+
+And the predicate:
+
+- is the number even?
+
+Then your keep operation should produce:
+
+- 2, 4
+
+While your discard operation should produce:
+
+- 1, 3, 5
+
+Note that the union of keep and discard is all the elements.
+
+The functions may be called `keep` and `discard`, or they may need different names in order to not clash with existing functions or concepts in your language.
+
+## Restrictions
+
+Keep your hands off that filter/reject/whatchamacallit functionality provided by your standard library!
+Solve this one yourself using other basic tools instead.

exercises/practice/strain/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "strain.jl"
+    ],
+    "test": [
+      "runtests.jl"
+    ],
+    "example": [
+      ".meta/example.jl"
+    ]
+  },
+  "blurb": "Implement the `keep` and `discard` operation on collections.",
+  "source": "Conversation with James Edward Gray II",
+  "source_url": "http://graysoftinc.com/"
+}

exercises/practice/strain/.meta/example.jl

@@ -0,0 +1,14 @@
+function keep(values, predicate)
+    results = []
+    for value in values
+        if predicate(value)
+            push!(results, value)
+        end
+    end
+
+    results
+end
+
+function discard(values, predicate)
+    keep(values, x -> !predicate(x))
+end

exercises/practice/strain/.meta/tests.toml

@@ -0,0 +1,52 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[26af8c32-ba6a-4eb3-aa0a-ebd8f136e003]
+description = "keep on empty list returns empty list"
+
+[f535cb4d-e99b-472a-bd52-9fa0ffccf454]
+description = "keeps everything"
+
+[950b8e8e-f628-42a8-85e2-9b30f09cde38]
+description = "keeps nothing"
+
+[92694259-6e76-470c-af87-156bdf75018a]
+description = "keeps first and last"
+
+[938f7867-bfc7-449e-a21b-7b00cbb56994]
+description = "keeps neither first nor last"
+
+[8908e351-4437-4d2b-a0f7-770811e48816]
+description = "keeps strings"
+
+[2728036b-102a-4f1e-a3ef-eac6160d876a]
+description = "keeps lists"
+
+[ef16beb9-8d84-451a-996a-14e80607fce6]
+description = "discard on empty list returns empty list"
+
+[2f42f9bc-8e06-4afe-a222-051b5d8cd12a]
+description = "discards everything"
+
+[ca990fdd-08c2-4f95-aa50-e0f5e1d6802b]
+description = "discards nothing"
+
+[71595dae-d283-48ca-a52b-45fa96819d2f]
+description = "discards first and last"
+
+[ae141f79-f86d-4567-b407-919eaca0f3dd]
+description = "discards neither first nor last"
+
+[daf25b36-a59f-4f29-bcfe-302eb4e43609]
+description = "discards strings"
+
+[a38d03f9-95ad-4459-80d1-48e937e4acaf]
+description = "discards lists"

exercises/practice/strain/runtests.jl

@@ -0,0 +1,146 @@
+using Test
+
+include("strain.jl")
+
+@testset verbose = true "tests" begin
+    @testset "keep" begin
+        @testset "keep on empty list returns empty list" begin
+            values = []
+            predicate = x -> true
+            result = keep(values, predicate)
+            expected = []
+            @test result == expected
+        end
+
+        @testset "keeps everything" begin
+            values = [1, 3, 5]
+            predicate = x -> true
+            result = keep(values, predicate)
+            expected = [1, 3, 5]
+            @test result == expected
+        end
+
+        @testset "keeps nothing" begin
+            values = [1, 3, 5]
+            predicate = x -> false
+            result = keep(values, predicate)
+            expected = []
+            @test result == expected
+        end
+
+        @testset "keeps first and last" begin
+            values = [1, 2, 3]
+            predicate = x -> x % 2 == 1
+            result = keep(values, predicate)
+            expected = [1, 3]
+            @test result == expected
+        end
+
+        @testset "keeps neither first nor last" begin
+            values = [1, 2, 3]
+            predicate = x -> x % 2 == 0
+            result = keep(values, predicate)
+            expected = [2]
+            @test result == expected
+        end
+
+        @testset "keeps strings" begin
+            values = ["apple", "zebra", "banana", "zombies", "cherimoya", "zealot"]
+            predicate = x -> startswith(x, 'z')
+            result = keep(values, predicate)
+            expected = ["zebra", "zombies", "zealot"]
+            @test result == expected
+        end
+
+        @testset "keeps lists" begin
+            values = [
+                [1, 2, 3],
+                [5, 5, 5],
+                [5, 1, 2],
+                [2, 1, 2],
+                [1, 5, 2],
+                [2, 2, 1],
+                [1, 2, 5]
+            ]
+            predicate = x -> in(5, x)
+            result = keep(values, predicate)
+            expected = [
+                [5, 5, 5],
+                [5, 1, 2],
+                [1, 5, 2],
+                [1, 2, 5]
+            ]
+            @test result == expected
+        end
+    end
+
+    @testset "discard" begin
+        @testset "discard on empty list returns empty list" begin
+            values = []
+            predicate = x -> true
+            result = discard(values, predicate)
+            expected = []
+            @test result == expected
+        end
+
+        @testset "discards everything" begin
+            values = [1, 3, 5]
+            predicate = x -> true
+            result = discard(values, predicate)
+            expected = []
+            @test result == expected
+        end
+
+        @testset "discards nothing" begin
+            values = [1, 3, 5]
+            predicate = x -> false
+            result = discard(values, predicate)
+            expected = [1, 3, 5]
+            @test result == expected
+        end
+
+        @testset "discards first and last" begin
+            values = [1, 2, 3]
+            predicate = x -> x % 2 == 1
+            result = discard(values, predicate)
+            expected = [2]
+            @test result == expected
+        end
+
+        @testset "discards neither first nor last" begin
+            values = [1, 2, 3]
+            predicate = x -> x % 2 == 0
+            result = discard(values, predicate)
+            expected = [1, 3]
+            @test result == expected
+        end
+
+        @testset "discards strings" begin
+            values = ["apple", "zebra", "banana", "zombies", "cherimoya", "zealot"]
+            predicate = x -> startswith(x, 'z')
+            result = discard(values, predicate)
+            expected = ["apple", "banana", "cherimoya"]
+            @test result == expected
+        end
+
+        @testset "discards lists" begin
+            values = [
+                [1, 2, 3],
+                [5, 5, 5],
+                [5, 1, 2],
+                [2, 1, 2],
+                [1, 5, 2],
+                [2, 2, 1],
+                [1, 2, 5]
+            ]
+            predicate = x -> in(5, x)
+            result = discard(values, predicate)
+            expected = [
+                [1, 2, 3],
+                [2, 1, 2],
+                [2, 2, 1]
+            ]
+            @test result == expected
+        end
+    end
+end

exercises/practice/strain/strain.jl

@@ -0,0 +1,7 @@
+function keep(values, predicate)
+
+end
+
+function discard(values, predicate)
+
+end