Julia “string” and methods()

Author(s): Vivek Chaudhary

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The objective of this article is to understand string-type variables in Julia Programming and various operations associated with them.

Strings in Julia are defined in “double quotes”.

1. Declare a string variable s1.

s1=”hello world”
println(s1)
print(typeof(s1)) #to check the datatype of variable

Output:
hello world
String

2. String Concatenation

s1=”hello vivek”
s2=”welcome to julia tutorial”

#using * operator
println(s1*’ ‘*s2)

#using string function
println(string(s1,’ ‘,s2))

Output:
"*": hello vivek welcome to julia tutorial
"string": hello vivek welcome to julia tutorial

3. String Index and Slicing

Index in Julia data types starts from 1 unlike python where it starts from 0

First, check what happens if we search for an item with Index 0.

println(s1[0])

Output:
BoundsError: attempt to access 40-codeunit String at index [0]

Stacktrace:
 [1] checkbounds
   @ .\strings\basic.jl:216 [inlined]
 [2] codeunit
   @ .\strings\string.jl:102 [inlined]
 [3] getindex(s::String, i::Int64)
   @ Base .\strings\string.jl:223
 [4] top-level scope
   @ In[4]:5
 [5] eval
   @ .\boot.jl:373 [inlined]
 [6] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
   @ Base .\loading.jl:1196

The usual way of searching items in a Julia string:

println(“item as pos 5 is“,s1[5])
println(“item as pos 9 is“,s1[9])

Output:
item as pos 5 is o
item as pos 9 is v

Slicing: Julia uses keywords “begin” and “end” to fetch the first and last item from a string.

s1=”hello vivek welcome to julia programming”

println("first item of string s1 is:",s1[begin])
println("last item of string s1 is:",s1[end])

Output:
first item of string s1 is: h
last item of string s1 is: g

#slicing
println(s1[begin:begin+10])
println(s1[begin+6:begin+18])
println(s1[begin:end-21])                                
println(s1[begin+6:length(s1)-12])

Output:
hello vivek
vivek welcome
hello vivek welcome
vivek welcome to julia

#negative Indexing
println(s1[end-3])
println(s1[7:end-12])
println(s1[end-10:end])

Output:
m
vivek welcome to julia
programming

4. String Interpolation

Interpolation is the process of executing whatever is executable in a string in Julia executable is mentioned by “$.”

s1=”vivek”
s2=”80"
println(“hello $s1, you scored $s2”)

Output:
hello vivek, you scored 80

5. String Comparison

println(cmp(“a”,”a”)) #returns 0 when output is true
println(cmp(“def”,”abc”)) #returns 1 when output is false

Output:
0
1

println(cmp('a',"a")) 
Output:
MethodError: no method matching isless(::Char, ::String)
Closest candidates are:
  isless(::AbstractString, ::AbstractString) at C:\Users\lenovo\AppData\Local\Programs\Julia-1.7.1\share\julia\base\strings\basic.jl:344
  isless(::Any, ::Missing) at C:\Users\lenovo\AppData\Local\Programs\Julia-1.7.1\share\julia\base\missing.jl:88
  isless(::Missing, ::Any) at C:\Users\lenovo\AppData\Local\Programs\Julia-1.7.1\share\julia\base\missing.jl:87
  ...

Stacktrace:
 [1] cmp(x::Char, y::String)
   @ Base .\operators.jl:467
 [2] top-level scope
   @ In[22]:2
 [3] eval
   @ .\boot.jl:373 [inlined]
 [4] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
   @ Base .\loading.jl:1196

‘single quotes’ represents char datatype
“double quotes” represents string type

6. String search operations

startswith()

s1=”hi geeks enjoying learning julia”
println(startswith(s1,’h’)) 
println(startswith(s1,’g’))

println(startswith(s1,”hi”))
println(startswith(s1,”julia”))

Output:
true
false
true
false

endswith()

s1=”hi geeks enjoying learning julia”
println(endswith(s1,’a’))
println(endswith(s1,’h’))

println(endswith(s1,”julia”))
println(endswith(s1,”learning”))

Output:
true
false
true
false

startswith() and endswith() can perform char and pattern searching.

findfirst() and findlast(): find the occurrence of the item and returns the position.

s1=”hi geeks enjoying learning julia”

#findfirst()
println(findfirst(‘j’,s1)) --> 12
println(findfirst(“geeks”,s1)) --> 4:8

#findlast()
println(findlast(‘j’,s1))  --> 28
println(findlast(‘e’,s1)) -->20

s2="hello vivek, Does vivek like julia?"

println("find vivek from first: ",findfirst("vivek",s2)) 
println("find vivek from last: ",findlast("vivek",s2))

Output:
find vivek from first: 7:11
find vivek from last: 19:23

findnext(): takes three arguments findnext(pattern,string,position to look from)

#findnext()
println(findnext(‘e’,s1,7))
println(findnext(‘j’,s1,findfirst(‘j’,s1)))

Output:
10
12

findprev()– takes three arguments findnext(pattern,string,position to look from)

#findprev()
println(findprev(‘e’,s1,18))

Output:
10

7. String strip

strip(), lstrip() and rstrip()

#strip()
println("length of string with whitespace: ",length("   vivek  "))
println("length of string without whitespace: ",length(strip("   vivek  ")))
println(strip("   vivek  "))
println(strip("sviveks",'s'))

Output:
length of string with whitespace: 10
length of string without whitespace: 5
vivek
vivek

#lstrip()
#lstrip
println("length of string with whitespace: ",length("   vivek  "))
println("length of string without whitespace: ",length(lstrip("   vivek  ")))
println(lstrip("  vivek",' '))
println(lstrip("sviveks",'s'))

Output:
length of string with whitespace: 10
length of string without whitespace: 7
vivek
viveks

#rstrip()
println("length of string with whitespace: ",length("   vivek  "))
println("length of string without whitespace: ",length(rstrip("   vivek  ")))
println(rstrip("  vivek",' '))
println(rstrip("sviveks",'s'))

Output:
length of string with whitespace: 10
length of string without whitespace: 8
  vivek
svivek

8. split() and join()

split() — separates the string into an array of items on the basis of a Separator.

join() — joins the array items to create a string

#split()

println(split("vivek#learning#julia#python",'#'))
#split the string into 3 array item
sprintln(split(“vivek learning julia and python”,’ ‘,limit=3))

Output:
SubString{String}["vivek", "learning", "julia", "python"]
SubString{String}["vivek", "learning", "julia and python"]

#join()

#join() similar to pythin join func
#join()- joins array of strings into string
l=["hello","julia","learners"]
println("joined string--> ",join(l,"##"))

Output:
joined string--> hello##julia##learners

9. substr()- to extract a part of the string

#substring()
s1="hi geeks enjoying learning julia"
println(SubString(s1,4,17))
println(SubString(s1,10,26))

Output:
geeks enjoying
enjoying learning

10. sort() — method works on an array of elements to sort the items in ascending or descending fashion. To sort a string, it is cast into an array using collect(), and then sort() is applied, and then it is converted back to a string using join().

#sort() and collect()
println("output of sort -->",sort(collect("vivek")))

println("sorted array converted back to string-->", join(sort(collect("vivek"))))

println("sorted array converted back to string reverse-->", join(sort(collect("vivek"),rev=true)))

Output:
output of sort -->['e', 'i', 'k', 'v', 'v']
sorted array converted back to string-->eikvv
sorted array converted back to string reverse-->vvkie

To Summarize:

• Julia strings and string methods.

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