update

crystal/arrays.md

@@ -1,9 +1,9 @@
 # Arrays
-{id: arrays}
+{id: array}
 
 
 ## Arrays intro
-{id: arrays-intro}
+{id: array-intro}
 
 * [Array API](https://crystal-lang.org/api/Array.html)
 * [Array reference](https://crystal-lang.org/reference/syntax_and_semantics/literals/array.html)
@@ -23,7 +23,7 @@
 ![](examples/arrays/array_iterate.cr)
 
 ## Array push, append, <<
-{id: arrays-push}
+{id: array-push}
 {i: push}
 {i: append}
 {i: <<}
@@ -38,12 +38,12 @@
 ![](examples/arrays/empty_array.cr)
 
 ## Count digitis
-{id: count-digits}
+{id: array-count-digits}
 
 ![](examples/arrays/count_digits.cr)
 
 ## Operations on arrays
-{id: operations-on-arrays}
+{id: array-operations}
 
 * add +
 * repeat *
@@ -94,7 +94,7 @@
 ![](examples/arrays/map.out)
 
 ## Sample from array
-{id: arrays-sample}
+{id: array-sample}
 {i: sample}
 
 * Using [Random](random) behind the scenes.
@@ -105,7 +105,7 @@
 
 
 ## Shuffle array
-{id: arrays-shuffle}
+{id: array-shuffle}
 {i: shuffle}
 
 * Using [Random](random) behind the scenes.
@@ -116,7 +116,7 @@
 
 
 ## join
-{id: arrays-join}
+{id: array-join}
 
 ![](examples/arrays/join.cr)
 
@@ -174,6 +174,12 @@
 ![](examples/arrays/uniq.cr)
 ![](examples/arrays/uniq.out)
 
+## First element of the array
+{id: array-first}
+{i: first}
+{i: first?}
+
+![](examples/arrays/first.cr)
 
 ## Permutations
 {id: array-permutations}

crystal/examples/arrays/first.cr

@@ -0,0 +1,15 @@
+names = ["Foo", "Bar"]
+puts names.first # Foo
+puts names[0]    # Foo
+
+names = [] of String
+# puts names.first
+# Unhandled exception: Empty enumerable (Enumerable::EmptyError)
+
+# puts names[0]
+# Unhandled exception: Index out of bounds (IndexError)
+
+first = names.first?
+puts first.nil? # true
+first = names[0]?
+puts first.nil? # true

crystal/examples/hashes/clear.cr

@@ -0,0 +1,8 @@
+planets = {
+  "Mars"    => 1,
+  "Jupyter" => 2,
+  "Saturn"  => 3,
+  "Earth"   => 4,
+}
+puts planets.clear # {}
+puts planets       # {}

crystal/examples/hashes/delete.cr

@@ -0,0 +1,8 @@
+planets = {
+  "Mars"    => 1,
+  "Jupyter" => 2,
+  "Saturn"  => 3,
+  "Earth"   => 4,
+}
+puts planets.delete("Mars")
+puts planets

crystal/examples/hashes/delete.out

@@ -0,0 +1,2 @@
+1
+{"Jupyter" => 2, "Saturn" => 3, "Earth" => 4}

crystal/examples/hashes/dig.cr

@@ -0,0 +1,19 @@
+planets = {
+  "Mars" => {
+    "Traveler" => "Elon",
+    "People"   => "Green",
+  },
+  "Jupyter" => 2,
+  "Saturn"  => 3,
+  "Earth"   => 4,
+}
+# puts planets["Mars"]["People"]
+# Error: undefined method '[]' for Int32 (compile-time type is (Hash(String, String) | Int32))
+
+puts planets.dig "Mars", "People" # Green
+
+# puts planets.dig "Mars", "Date"
+# Unhandled exception: Missing hash key: "Date" (KeyError)
+
+date = puts planets.dig? "Mars", "Date" # nil
+puts date.nil?                          # true

crystal/examples/hashes/multi_dimensional.cr

@@ -0,0 +1,22 @@
+planets = {
+  "Mars" => {
+    "color" => "Red, brown and tan.",
+  },
+  "Jupyter" => {
+    "color" => "Brown, orange and tan, with white cloud stripes.",
+  },
+  "Saturn" => {
+    "color" => "Golden, brown, and blue-grey.",
+  },
+  "Earth" => {
+    "color" => "Blue, brown green and white.",
+  },
+}
+
+puts planets["Mars"]["color"]
+
+# puts planets["Mercury"]
+# Unhandled exception: Missing hash key: "Mercury" (KeyError)
+
+# puts planets["Mars"]["rover"]
+# Unhandled exception: Missing hash key: "rover" (KeyError)

crystal/examples/hashes/reject.cr

@@ -0,0 +1,11 @@
+planets = {
+  "Mars"    => 1,
+  "Jupyter" => 2,
+  "Saturn"  => 3,
+  "Earth"   => 4,
+}
+puts planets.reject("Mars")
+puts planets
+
+puts planets.reject!("Mars")
+puts planets

crystal/examples/hashes/reject.out

@@ -0,0 +1,4 @@
+{"Jupyter" => 2, "Saturn" => 3, "Earth" => 4}
+{"Mars" => 1, "Jupyter" => 2, "Saturn" => 3, "Earth" => 4}
+{"Jupyter" => 2, "Saturn" => 3, "Earth" => 4}
+{"Jupyter" => 2, "Saturn" => 3, "Earth" => 4}

crystal/examples/hashes/select.cr

@@ -0,0 +1,12 @@
+planets = {
+  "Mars"    => 1,
+  "Jupyter" => 2,
+  "Saturn"  => 3,
+  "Earth"   => 4,
+}
+
+puts planets.select { |name, number| number > 2 && name.includes?("r") }
+puts planets
+
+puts planets.select! { |name, number| number > 2 && name.includes?("r") }
+puts planets

crystal/examples/hashes/select.out

@@ -0,0 +1,4 @@
+{"Saturn" => 3, "Earth" => 4}
+{"Mars" => 1, "Jupyter" => 2, "Saturn" => 3, "Earth" => 4}
+{"Saturn" => 3, "Earth" => 4}
+{"Saturn" => 3, "Earth" => 4}

crystal/hashes.md

@@ -54,3 +54,47 @@
 ![](examples/hashes/merge.cr)
 ![](examples/hashes/merge.out)
 
+## Delete - remove an element from a hash
+{id: hash-delete}
+{i: delete}
+
+* `delete!` does not exist.
+
+![](examples/hashes/delete.cr)
+![](examples/hashes/delete.out)
+
+
+## Reject - remove an element from a hash
+{id: hash-reject}
+{i: reject}
+{i: reject!}
+
+![](examples/hashes/reject.cr)
+![](examples/hashes/reject.out)
+
+## Clear - empty a hash
+{id: hash-clear}
+{i: clear}
+
+![](examples/hashes/clear.cr)
+
+## Select - keep certain key-value pairs
+{id: hash-select}
+{i: select}
+{i: select!}
+
+![](examples/hashes/select.cr)
+![](examples/hashes/select.out)
+
+## Multi-dimensional hash
+{id: hash-multi-dimensional}
+
+![](examples/hashes/multi_dimensional.cr)
+
+## Dig a hash
+{id: hash-dig}
+{i: dig}
+{i: dig?}
+
+![](examples/hashes/dig.cr)
+

crystal/other.md

@@ -205,3 +205,7 @@ require "some_name"         # Find it somewhere (standard library, src directory
 * [Crystal Weekly](https://crystalweekly.com/)
 * [Friends of Crystal](https://friendsofcrystal.com/)
 
+* [Facebook page](https://www.facebook.com/Crystallang-1457045254320264/)
+* [Facebook group](https://www.facebook.com/groups/crystallang/)
+* [LinkedIn page](https://www.linkedin.com/company/crystal-language/)
+