add Enum.sum_by/2

Author: superruzafa

assets/images/functions/Enum/sum_by-2.tex

@@ -0,0 +1,22 @@
+\matrix [list=a] {
+  \node [index=1]; &
+  \node [index=2]; &
+  \node [elements between]; &
+  \node [index=n]; \\
+};
+
+\foreach \i in {1,2,n}{
+    \node (fun\i) [fun, below=.5 of a\i.south];
+    \draw [->] (a\i.south) -- (fun\i.in);
+    \draw [->] (fun\i.out) -- +(0, -.5)
+        node (b\i) [below] {$b_{\i}$};
+};
+
+
+
+\draw [brace] (bn.south east) -- (b1.south west);
+
+\draw [->] (last brace) -- +(0, -1)
+  node [below]
+  {$b_1 + b_2 + \dots + b_n = \displaystyle\sum_{i=1}^n b_i$};
+ 

content/en/functions/Enum/sum_by-2.md

@@ -0,0 +1,10 @@
+---
+title: sum_by/2
+url: Enum/sum_by/2
+---
+
+Maps and computes the sum of the given `enumerable` in one pass.
+
+Raises `ArithmeticError` if `fun` returns a non-numeric value.
+
+{{< figure src="images/functions/Enum/sum_by-2.svg" >}}

data/signatures.yaml

@@ -364,6 +364,11 @@
         defmodule Enum do
           def sum(enumerable)
         end
+    - name: sum_by/2
+      signature: |
+        defmodule Enum do
+          def sum_by(enumerable, fun)
+        end
     - name: take/2
       signature: |
         defmodule Enum do