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Slices 02-201
![Page 1: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/1.jpg)
Slices 02-201
![Page 2: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/2.jpg)
Issue with Implementing PrimeSieve() in Go
func PrimeSieve(n int) [n+1]bool {var isComposite [n+1]bool //ERROR!biggestPrime := 2for biggestPrime < n
for i:=2; i<=n/biggestPrime; i++ {isComposite[i+biggestPrime] = true
}biggestPrime++for biggestPrime<n &&isComposite[biggestPrime]{
biggestPrime++}
return isComposite}
Go only allows us to create an array of constant size.
![Page 3: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/3.jpg)
var a []int// at this point a has the special value nil// and can’t be used as an arraya = make([]int, 10, 20)
0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0!0! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10! 11! 12! 13! 14! 15! 16! 17! 18! 19!
Underlying array has size 20!
Length of this slice is 10!
A slice variable is declared by not specifying a size in []
Creates an array of size 20 with a slice of size 10 inside it.
Slices: Everything Arrays Should Be
![Page 4: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/4.jpg)
Omitting the Third Parameter
var a []inta = make([]int, 10)// this is the same as make([]int, 10, 10)
![Page 5: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/5.jpg)
We Can Still Change Items
var a []inta = make([]int, 10)a[3] = -18a[9] = 100a[10] = 1 //error: out of range
![Page 6: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/6.jpg)
Passing a Variable as Slice Length
m := 100var b []stringb = make([]string, m) // this is OK!
![Page 7: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/7.jpg)
Defining a Slice in One Line
m := 100b := make([]string, m) // this is OK!
![Page 8: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/8.jpg)
String literals: a sequence of characters between “”
“Hi there”“😄”“1+㆔=4”“3.14159”
Integer literals: a sequence of digits 0…9
726402000734
bool (Boolean) literals: either true or false
truefalse
Unicode strings are supported.
Recall: Literals ... The Other Side of “=”
![Page 9: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/9.jpg)
We can manually create slices (useful if you have a short list of data that may change):
Array and Slice Literals
var a = []float64{3.2, -30.1, 84.72, 62.0}var prime = []int{2,3,5,7,11}
var b = [3]float64{2.8, -30.1, 13.2}var odds = [4]int{1,3,5,7}
We can also use array literals (useful for a short list of data that is fixed):
![Page 10: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/10.jpg)
Fixing PrimeSieve
func PrimeSieve(n int) []bool {isComposite := make([]bool, n+1) //Fixed!biggestPrime := 2for biggestPrime < n
for i:=2; i<=n/biggestPrime; i++ {isComposite[i+biggestPrime] = true
}biggestPrime++for biggestPrime<n && isComposite[biggestPrime]{
biggestPrime++}
return isComposite}
![Page 11: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/11.jpg)
func Max(A [10000000]int) int { m := 0 for i := range A { if i == 0 || A[i] > m { m = A[i] } } return m}
func main() { var numbers [10000000]int
// fill numbers with random integers for i := range numbers { numbers[i] = rand.Int() }
fmt.Println(Max(numbers))}
A new array A is created and the contents from numbers is copied over (wasteful of memory).
Issue #2: Arrays Copied in Function Calls
![Page 12: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/12.jpg)
Passing a Slice as an Argument
We can also pass a slice (of unknown length) as a function argument.
func Max(list []int) int {var m int = list[0]for i := range list {
if list[i] > m {m = list[i]
}}return m
}
![Page 13: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/13.jpg)
Passing a Slice as an Argument
func Fudge1(list []int) {list[0] = 1
}
func Fudge2(list [100]int) {list[0] = 1
}
![Page 14: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/14.jpg)
Passing a Slice as an Argument
func Fudge1(list []int) {list[0] = 1
}
Exercise: What is printed in main()?
func Fudge2(list [100]int) {list[0] = 1
}
func main() {list1 := make([]int, 100)var list2 [100]intFudge1(list1)Fudge2(list2)fmt.Println(list1[0], list2[0])
}
![Page 15: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/15.jpg)
Passing a Slice as an Argument
func Fudge1(list []int) {list[0] = 1
}
Exercise: What is printed in main()?
func Fudge2(list [100]int) {list[0] = 1
}
func main() {list1 := make([]int, 100)var list2 [100]intFudge1(list1)Fudge2(list2)fmt.Println(list1[0], list2[0])
}
Answer: 1 0
![Page 16: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/16.jpg)
Looping Over Both Indices and Elements
“range” also lets us loop over both the index and the elements of a slice.
func Max(list []int) int {var m intfor j, v := range list {
if j == 0 || v > m {m = v
}}return m
}
![Page 17: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/17.jpg)
The Blank Identifier
func Sum(A []int) int { var result int for i, val := range A { result = result + val } return result}
Think: What is the issue here?
![Page 18: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/18.jpg)
The Blank Identifier
func Sum(A []int) int { var result int for i, val := range A { result = result + val } return result}
Error! Variable i declared and never used.
![Page 19: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/19.jpg)
The Blank Identifier
func Sum(A []int) int { var result int for i, val := range A { result = result + val } return result}
func Sum(A []int) int { var result int for _, val := range A { result = result + val } return result}
Error! Variable i declared and never used.
Blank identifier _ (single underscore) is useful when declaring a variable that is never used.
![Page 20: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/20.jpg)
Recall: Substrings in Go
s := “Hi There!”fmt.Println(s[3:5]) // prints Thfmt.Println(s[1:]) // prints i There!fmt.Println(s[:4]) // prints Hi T
var str string = s[3:6]fmt.Println(str) // prints Thefmt.Println(str[0]) // prints T
H i T h e r e !0 1 2 3 4 5 6 7 8
“Subslicing” works in the same way.
![Page 21: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/21.jpg)
s := make([]int, 10, 20)for i:=1; i<10; i++ {
s[i] = -i - 1}
array!
start! 0!end! 9!
-1! -2! -3! -4! -5! -6! -7! -8! -9! -10! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0!0! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10! 11! 12! 13! 14! 15! 16! 17! 18! 19!
Subslices: A Picture
s!
![Page 22: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/22.jpg)
s := make([]int, 10, 20)for i:=1; i<10; i++ {
s[i] = -i - 1}var q []int = s[8:15]
array!
start! 0!end! 9!
array!
start! 8!end! 14!
-1! -2! -3! -4! -5! -6! -7! -8! -9! -10! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0!0! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10! 11! 12! 13! 14! 15! 16! 17! 18! 19!
Subslices: A Picture
s! q !
![Page 23: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/23.jpg)
s := make([]int, 10, 20)for i:=1; i<10; i++ {
s[i] = -i - 1}var q []int = s[8:15]
array!
start! 0!end! 9!
array!
start! 8!end! 14!
-1! -2! -3! -4! -5! -6! -7! -8! -9! -10! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0!0! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10! 11! 12! 13! 14! 15! 16! 17! 18! 19!
Subslices: A Picture
s! q !
len(q) == 7fmt.Println(q[0]) // -9fmt.Println(q[6]) // -15fmt.Println(q[15]) // ERRORs[8] == q[0]s[9] = 12 // now q[1] == 12 too!
Both slices refer to the same underlying array.
![Page 24: Slices - Phillip Compeaucompeau.cbd.cmu.edu/wp-content/uploads/2016/08/lec_12.pdf · var a = []float64{3.2, -30.1, 84.72, 62.0} var prime = []int{2,3,5,7,11} var b = [3]float64{2.8,](https://reader034.documents.pub/reader034/viewer/2022050411/5f882cabe91c4f1d6f284fa8/html5/thumbnails/24.jpg)
The append() and copy() Operations
s := make([]int, 10)s = append(s, 5)
0! 0! 0! 0! 0 0! 0! 0! 0 0! 50! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10
c := make([]int, 11)copy(c, s)
0! 0! 0! 0! 0 0! 0! 0! 0 0! 5!0! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10!
s!
c!
![MLRG: Basic Monte Carlo Methods - cs.ubc.ca · Var( ) = E[Var( jY)] + Var(E[ jY]) =)Var( ) Var(E[ jY]) If E[ ] is the quantity we wish to approximate, then we can use E[ jY] instead](https://static.documents.pub/doc/80x56/5f3ec4f2b30bfe38ed1927ea/mlrg-basic-monte-carlo-methods-csubcca-var-evar-jy-vare-jy-var.jpg)
![Welcome [tc18.tableau.com] · 2020. 1. 6. · var css_pp = pd.css(data); var css_min = pd.cssmin(data [, true]); var sql_pp = pd.sql(data); var sql_min = pd.sqlmin(data); Click to](https://static.documents.pub/doc/80x56/603a266b2957ea033f3cea48/welcome-tc18-2020-1-6-var-csspp-pdcssdata-var-cssmin-pdcssmindata.jpg)
