Prepare repository for merge

python/snippets/sum-by.md

@@ -0,0 +1,21 @@
+---
+title: Sum list based on function
+type: snippet
+tags: [math,list]
+cover: horse-sunset
+dateModified: 2020-11-02T19:28:35+02:00
+---
+
+Calculates the sum of a list, after mapping each element to a value using the provided function.
+
+- Use `map()` with `fn` to map each element to a value using the provided function.
+- Use `sum()` to return the sum of the values.
+
+```py
+def sum_by(lst, fn):
+  return sum(map(fn, lst))
+```
+
+```py
+sum_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda v : v['n']) # 20
+```