v/vlib/arrays/arrays.v

module arrays

// Common arrays functions:
// - min / max - return the value of the minumum / maximum
// - idx_min / idx_max - return the index of the first minumum / maximum
// - shuffle - randomize array items order in place (allowing exit after n items)
// - merge - combine two sorted arrays and maintain sorted order

import rand

// min returns the minimum
[direct_array_access]
pub fn min<T>(a []T) T {
	if a.len==0 { panic('.min called on an empty array') }
	mut val := a[0]
	for i in 0..a.len {
		if a[i] < val {
			val = a[i]
		}
	}
	return val
}

// max returns the maximum
[direct_array_access]
pub fn max<T>(a []T) T {
	if a.len==0 { panic('.max called on an empty array') }
	mut val := a[0]
	for i in 0..a.len {
		if a[i] > val {
			val = a[i]
		}
	}
	return val
}

// idx_min returns the index of the first minimum
[direct_array_access]
pub fn idx_min<T>(a []T) int {
	if a.len==0 { panic('.idxmin called on an empty array') }
	mut idx := 0
	mut val := a[0]
	for i in 0..a.len {
		if a[i] < val {
			val = a[i]
			idx = i
		}
	}
	return idx
}

// idx_max returns the index of the first maximum
[direct_array_access]
pub fn idx_max<T>(a []T) int {
	if a.len==0 { panic('.idxmax called on an empty array') }
	mut idx := 0
	mut val := a[0]
	for i in 0..a.len {
		if a[i] > val {
			val = a[i]
			idx = i
		}
	}
	return idx
}

// shuffle randomizes the first n items of an array in place (all if n=0)
[direct_array_access]
pub fn shuffle<T>(mut a []T, n int) {
	if n < 0 || n > a.len { panic("shuffle's argument 'n' must be in range [0,a.len]") }
	cnt := if n==0 { a.len-1 } else { n }
	for i in 0..cnt {
		x := rand.int_in_range(i,a.len)
		// swap
		a_i := a[i]
		a[i] = a[x]
		a[x] = a_i
	}
}


// merge two sorted arrays (ascending) and maintain sorted order
[direct_array_access]
pub fn merge<T>(a []T, b []T) []T {
	mut m := []T{len:a.len + b.len}
	mut ia := 0
	mut ib := 0
	mut j := 0
	
	// TODO efficient approach to merge_desc where: a[ia] >= b[ib]
	for ia<a.len && ib<b.len {
		if a[ia] <= b[ib] {
			m[j] = a[ia]
			ia++
		} else {
			m[j] = b[ib]
			ib++
		}
		j++
	}
	
	// a leftovers
	for ia < a.len {
		m[j] = a[ia]
		ia++
		j++
	}
	
	// b leftovers
	for ib < b.len {
		m[j] = b[ib]
		ib++
		j++
	}
	
	return m
}