suggested edits to the learn Julia in Y minutes document.

This commit is contained in:
Stefan Karpinski 2013-07-02 23:15:34 -04:00
parent 0cf568d278
commit bbfe94770f

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