10.2. String Functions

Julia defines a number of functions that operate on strings. For example, lowercase and uppercase converts all letters to lower- or upper-case:

println(uppercase("julia123 ") * lowercase("LOWER"))

JULIA123 lower

The titlecase commands capitalizes the first character of each word in a string:

str = "SEARCHING FOR CHARACTERS AND SUBSTRINGS"
titlecase(str)

"Searching For Characters And Substrings"

10.2.1. Searching for characters and substrings

The ∈ operator (type “\in” and tab) returns true if a characters appears in a string:

'!' ∈ str

false

The function findfirst(pattern, str) returns the indices of the first occurance of pattern in str:

str = "Hello, World! These are my words."
pattern = "wor"
idx1 = findfirst(pattern, lowercase(str))

8:10

The function findnext(pattern, str, start) returns the indicies of the next occurance of pattern in str after the one at position start:

idx2 = findnext(pattern, lowercase(str), idx1[end])

28:30

Similarly, findlast and findprev starts from the end of the string.

10.2.2. Replacing substrings

The function replace(str, pattern=>repl) searches the string str for all occurances of the substring pattern, and replace them with the string repl:

println(str)
println(replace(str, ", World"=>" there"))

Hello, World! These are my words.
Hello there! These are my words.

10.2.3. Converting strings

The function parse(Type, string; base) lets you parse a string that contains a number into the actual number.

parse(Int, "1234")

1234

parse(Int, "011010", base = 2)

26

parse(Float64, "1.2e-3")

0.0012

This function is particularly useful when parsing input files containing numbers.

strings = ["123.4", "4590.12", "0.456"]
parse.(Float64, strings)

3-element Vector{Float64}:
  123.4
 4590.12
    0.456