Inject vs each_with_object in ruby

Author: Rajeev N B

ruby/inject_vs_each_with_object.md

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+# Inject vs each_with_object
+
+## Inject
+
+Inject takes the value of the block and passes it along.
+This causes a lot of errors like.
+
+```ruby
+  inject_array = ['A', 'B', 'C', 'D']
+
+  inject_array.inject({}) do |accumulator, value|
+    accumulator[value] = value.downcase
+  end
+  
+  Output: 'IndexError: string not matched'
+```
+
+The above code causes 'IndexError: string not matched' error.
+
+What you really wanted.
+
+```ruby
+  inject_array = ['A', 'B', 'C', 'D']
+
+  inject_array.inject({}) do |accumulator, value|
+    accumulator[value] = value.downcase
+    accumulator
+  end
+
+  Output: => {"A"=>"a", "B"=>"b", "C"=>"c", "D"=>"d"}
+  ```
+
+## each_with_object
+
+  each_with_object ignores the return value of the block and passes the initial object along.
+
+```ruby
+  array = ['A', 'B', 'C', 'D']
+
+  array.each_with_object({}) do |value, accumulator|
+    accumulator[value] = value.downcase
+  end
+
+  Output: => {"A"=>"a", "B"=>"b", "C"=>"c", "D"=>"d"}
+  ```
+One more thing which you can notice is the order of arguments to the block for each of the functions.
+
+Inject takes the result/accumulator and then the iteratable value, whereas 'each_with_object' takes the value followed by the result/accumulator.