arrays: common methods - min, max, idx_min, idx_max, shuffle, merge (#6177)

vlib/arrays/arrays.v

@@ -0,0 +1,118 @@
+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
+}
+

vlib/arrays/arrays_test.v

@@ -0,0 +1,97 @@
+module arrays
+
+import rand
+
+fn test_min() {
+	a := [8, 2, 6, 4]
+	assert min<int>(a)==2
+	assert min<int>(a[2..])==4
+	
+	b := [f32(5.1), 3.1, 1.1, 9.1]
+	assert min<f32>(b) == f32(1.1)
+	assert min<f32>(b[..2]) == f32(3.1)
+	
+	c := [byte(4), 9, 3, 1]
+	assert min<byte>(c) == byte(1)
+	assert min<byte>(c[..3]) == byte(3)
+}
+
+
+fn test_max() {
+	a := [8, 2, 6, 4]
+	assert max<int>(a)==8
+	assert max<int>(a[1..])==6
+	
+	b := [f32(5.1), 3.1, 1.1, 9.1]
+	assert max<f32>(b) == f32(9.1)
+	assert max<f32>(b[..3]) == f32(5.1)
+	
+	c := [byte(4), 9, 3, 1]
+	assert max<byte>(c) == byte(9)
+	assert max<byte>(c[2..]) == byte(3)
+}
+
+
+fn test_idx_min() {
+	a := [8, 2, 6, 4]
+	assert idx_min<int>(a)==1
+	
+	b := [f32(5.1), 3.1, 1.1, 9.1]
+	assert idx_min<f32>(b) == 2
+	
+	c := [byte(4), 9, 3, 1]
+	assert idx_min<byte>(c) == 3
+}
+
+
+fn test_idx_max() {
+	a := [8, 2, 6, 4]
+	assert idx_max<int>(a)==0
+	
+	b := [f32(5.1), 3.1, 1.1, 9.1]
+	assert idx_max<f32>(b) == 3
+	
+	c := [byte(4), 9, 3, 1]
+	assert idx_max<byte>(c) == 1
+}
+
+
+fn test_shuffle() {
+	rand.seed([u32(1),2]) // set seed to produce same results in order
+
+	a := [1,2,3,4,5,6,7,8,9,10]
+	mut b := a.clone()
+	mut c := a.clone()
+	shuffle<int>(mut b, 0)
+	shuffle<int>(mut c, 0)
+	assert b == [6, 4, 5, 1, 9, 2, 10, 3, 8, 7]
+	assert c == [1, 6, 5, 8, 7, 2, 10, 9, 3, 4]
+
+	// test shuffling a slice
+	mut d := a.clone()
+	shuffle<int>(mut d[..5], 0)
+	assert d == [5, 2, 1, 3, 4, 6, 7, 8, 9, 10]
+	assert d[5..] == a[5..]
+
+	// test shuffling n items
+	mut e := a.clone()
+	shuffle<int>(mut e, 5)
+	assert e[..5] == [10, 3, 1, 8, 4]
+	assert e[5..] == [6, 7, 5, 9, 2]
+
+	// test shuffling empty array
+	mut f := a[..0]
+	shuffle<int>(mut f,0)
+	assert f == []int{}
+}
+
+fn test_merge() {
+	a := [1,3,5,5,7]
+	b := [2,4,4,5,6,8]
+	c := []int{}
+	d := []int{}
+	assert merge<int>(a,b) == [1,2,3,4,4,5,5,5,6,7,8]
+	assert merge<int>(c,d) == []
+	assert merge<int>(a,c) == a
+	assert merge<int>(d,b) == b
+}