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suggested edits to the learn Julia in Y minutes document.
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Stefan Karpinski
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@ -51,6 +51,15 @@ div(5, 2) #=> 2
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bits(2) #=> "0000000000000000000000000000000000000000000000000000000000000010"
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bits(2.0) #=> "0100000000000000000000000000000000000000000000000000000000000000"
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# this might be a better example:
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julia> bits(123)
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"0000000000000000000000000000000000000000000000000000000001111011"
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julia> bits(123.0)
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"0100000001011110110000000000000000000000000000000000000000000000"
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# the other one stands the risk of someone thinking that floating-point
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# numbers are just integers with reversed bit-patterns or something.
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# Boolean values are primitives
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true
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false
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@ -80,7 +89,7 @@ false
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"This is a string"[1] #=> 'T' # Julia indexes from 1
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# $ can be used for string interpolation:
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"2 + 2 = $(2+2)" # => "2 + 2 = 4"
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"2 + 2 = $(2 + 2)" #=> "2 + 2 = 4"
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# You can put any Julia expression inside the parenthesis.
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# Another way to format strings is the printf macro.
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@ -100,7 +109,7 @@ some_var #=> 5
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some_other_var #=> ERROR: some_other_var not defined
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# Variable Names:
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SomeOtherVar123! = 6 #=> 6 # You can use uppercase letters, digits, and exclamation points as well.
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SomeOtherVar123! = 6 #=> 6 # You can use uppercase letters, digits, and exclamation points as well after the initial alphabetic character.
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☃ = 8 #=> 8 # You can also use unicode characters
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# A note on naming conventions in Julia:
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@ -109,26 +118,28 @@ SomeOtherVar123! = 6 #=> 6 # You can use uppercase letters, digits, and exclamat
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# * Names of functions and macros are in lower case, without underscores.
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# * Functions that modify their inputs have names that end in !. These functions are sometimes called mutating functions or in-place functions.
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# Arrays store sequences
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li = Int64[] #=> 0-element Int64 Array
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# Arrays store a sequence of values indexed by integers 1 through n:
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a = Int64[] #=> 0-element Int64 Array
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# 1-dimensional array literals can be written with comma-separated values.
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other_li = [4, 5, 6] #=> 3-element Int64 Array: [4, 5, 6]
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b = [4, 5, 6] #=> 3-element Int64 Array: [4, 5, 6]
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b[1] #=> 4
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b[end] #=> 6
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# 2-dimentional arrays use space-separated values and semicolon-separated rows.
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matrix = [1 2; 3 4] #=> 2x2 Int64 Array: [1 2; 3 4]
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# Add stuff to the end of a list with push! and append!
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push!(li,1) #=> [1]
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push!(li,2) #=> [1,2]
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push!(li,4) #=> [1,2,4]
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push!(li,3) #=> [1,2,4,3]
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append!(li,other_li) #=> [1,2,4,3,4,5,6]
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push!(a,1) #=> [1]
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push!(a,2) #=> [1,2]
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push!(a,4) #=> [1,2,4]
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push!(a,3) #=> [1,2,4,3]
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append!(a,b) #=> [1,2,4,3,4,5,6]
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# Remove from the end with pop
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pop!(other_li) #=> 6 and other_li is now [4,5]
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pop!(a) #=> 6 and b is now [4,5]
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# Let's put it back
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push!(other_li,6) # other_li is now [4,5,6] again.
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push!(b,6) # b is now [4,5,6] again.
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li[1] #=> 1 # remember that Julia indexes from 1, not 0!
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li[end] #=> 6 # end is a shorthand for the last index; it can be used in any indexing expression.
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a[1] #=> 1 # remember that Julia indexes from 1, not 0!
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a[end] #=> 6 # end is a shorthand for the last index; it can be used in any indexing expression.
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# Function names that end in exclamations points indicate that they modify their argument.
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arr = [5,4,6] #=> 3-element Int64 Array: [5,4,6]
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@ -136,36 +147,37 @@ sort(arr) #=> [4,5,6]; arr is still [5,4,6]
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sort!(arr) #=> [4,5,6]; arr is now [4,5,6]
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# Looking out of bounds is a BoundsError
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li[0] # ERROR: BoundsError() in getindex at array.jl:270
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a[0] #=> ERROR: BoundsError() in getindex at array.jl:270
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a[end+1] #=> ERROR: BoundsError() in getindex at array.jl:270
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# Errors list the line and file they came from, even if it's in the standard library.
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# If you built Julia from source, you can look in the folder base inside the julia folder to find these files.
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# You can initialize arrays from ranges
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li = [1:5] #=> 5-element Int64 Array: [1,2,3,4,5]
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a = [1:5] #=> 5-element Int64 Array: [1,2,3,4,5]
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# You can look at ranges with slice syntax.
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li[1:3] #=> [1, 2, 3]
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a[1:3] #=> [1, 2, 3]
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# Omit the beginning
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li[2:] #=> [2, 3, 4, 5]
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a[2:] #=> [2, 3, 4, 5]
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# Remove arbitrary elements from a list with splice!
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arr = [3,4,5]
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splice!(arr,2) #=> 4 ; arr is now [3,5]
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# Concatenate lists with append!
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other_li = [1,2,3]
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append!(li,other_li) # Now li is [1, 3, 4, 5, 1, 2, 3]
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b = [1,2,3]
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append!(a,b) # Now a is [1, 3, 4, 5, 1, 2, 3]
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# Check for existence in a list with contains
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contains(li,1) #=> true
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contains(a,1) #=> true
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# Examine the length with length
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length(li) #=> 7
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length(a) #=> 7
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# Tuples are immutable.
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tup = (1, 2, 3) #=>(1,2,3) # an (Int64,Int64,Int64) tuple.
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tup[1] #=> 1
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tup[0] = 3 # ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
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tup[0] = 3 #=> ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
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# Many list functions also work on tuples
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length(tup) #=> 3
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@ -190,8 +202,7 @@ filled_dict["one"] #=> 1
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# Get all keys
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keys(filled_dict) #=> KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
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# Note - Dictionary key ordering is not guaranteed.
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# Your results might not match this exactly.
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# Note - dictionary keys are not sorted or in the order you inserted them.
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# Get all values
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values(d) #=> ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
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@ -243,12 +254,11 @@ if some_var > 10
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println("some_var is totally bigger than 10.")
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elseif some_var < 10 # This elseif clause is optional.
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println("some_var is smaller than 10.")
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else # This is optional too.
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else # The else clause is optional too.
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println("some_var is indeed 10.")
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end
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# For loops iterate over iterable things, such as ranges, lists, sets, dicts, strings.
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# prints:
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# dog is a mammal
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@ -308,7 +318,7 @@ function add(x, y)
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x + y # or equivalently: return x + y
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end
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add(5, 6) #=> 11 and prints out "x is 5 and y is 6"
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add(5, 6) #=> 11 after printing out "x is 5 and y is 6"
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# You can define functions that take a variable number of
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# positional arguments
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@ -316,13 +326,13 @@ function varargs(args...)
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return args
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end
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varargs(1, 2, 3) #=> (1,2,3)
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varargs(1,2,3) #=> (1,2,3)
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# The ... is called a splat.
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# It can also be used in a fuction call
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# to splat a list or tuple out to be the arguments
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Set([1,2,3]) #=>Set{Array{Int64,1}}([1,2,3]) # no ..., produces a Set of Arrays
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Set([1,2,3]...) #=>Set{Int64}(1,2,3) # this is equivalent to Set(1,2,3)
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Set([1,2,3]) #=> Set{Array{Int64,1}}([1,2,3]) # no ..., produces a Set of Arrays
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Set([1,2,3]...) #=> Set{Int64}(1,2,3) # this is equivalent to Set(1,2,3)
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x = (1,2,3) #=> (1,2,3)
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Set(x) #=> Set{(Int64,Int64,Int64)}((1,2,3)) # a Set of Tuples
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@ -331,7 +341,7 @@ Set(x...) #=> Set{Int64}(2,3,1)
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# You can define functions with optional positional arguments
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function defaults(a,b,x=5,y=6)
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return "$a $b and $x $y"
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return "$a $b and $x $y"
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end
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defaults('h','g') #=> "h g and 5 6"
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@ -364,10 +374,10 @@ all_the_args(1, 3, keyword_arg=4)
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# Julia has first class functions
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function create_adder(x)
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adder = function (y)
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return x + y
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end
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return adder
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adder = function (y)
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return x + y
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end
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return adder
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end
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# or equivalently
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@ -377,10 +387,10 @@ end
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# you can also name the internal function, if you want
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function create_adder(x)
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function adder(y)
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x + y
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end
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adder
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function adder(y)
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x + y
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end
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adder
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end
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add_10 = create_adder(10)
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@ -394,8 +404,8 @@ map(add_10, [1,2,3]) #=> [11, 12, 13]
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filter(x -> x > 5, [3, 4, 5, 6, 7]) #=> [6, 7]
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# We can use list comprehensions for nice maps and filters
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[add_10(i) for i=[1, 2, 3]] #=> [11, 12, 13]
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[add_10(i) for i in [1, 2, 3]] #=> [11, 12, 13]
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[add_10(i) for i=[1, 2, 3]] #=> [11, 12, 13]
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[add_10(i) for i in [1, 2, 3]] #=> [11, 12, 13]
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####################################################
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## 5. Types and Multiple-Dispatch
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@ -462,4 +472,3 @@ pet_cat(Lion(Panther(),"42")) #=> prints "The cat says 42"
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You can get a lot more detail from [The Julia Manual](http://docs.julialang.org/en/latest/manual/)
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