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perf: improve GroupBy map initialization

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Fixes useless capacity hint of 0 for map initialization.
Uses estimated capacity of len(values)/10 to reduce map
resizing operations.

Changes:
- Before: make(map[K][]V, 0) - capacity 0 is meaningless for maps
- After: make(map[K][]V, len(values)/10) - reasonable estimate

Impact:
- Reduces map resizing overhead during population
- Assumes ~10% unique keys (reasonable for grouping operations)
- May over-allocate for high cardinality, but acceptable trade-off

This is a minor optimization that avoids repeated map growth
when keys are added.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
This commit is contained in:
Ruidy 2025-11-14 14:32:05 +01:00
parent 75eddcdde5
commit 07d05425bb
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groupby.go
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@ -2,7 +2,7 @@ package underscore
// GroupBy splits a slice into a map[K][]V grouped by the result of the iterator function. // GroupBy splits a slice into a map[K][]V grouped by the result of the iterator function.
func GroupBy[K comparable, V any](values []V, f func(V) K) map[K][]V { func GroupBy[K comparable, V any](values []V, f func(V) K) map[K][]V {
res := make(map[K][]V, 0) res := make(map[K][]V, len(values)/10)
for _, v := range values { for _, v := range values {
k := f(v) k := f(v)
if r, ok := res[k]; ok { if r, ok := res[k]; ok {