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authorMartijn Visser <mgvisser@gmail.com>2018-08-15 16:54:03 +0200
committerMartijn Visser <mgvisser@gmail.com>2018-08-15 16:54:03 +0200
commit9fab30a26a0de8603b19b95055f68af031c906bb (patch)
tree7f16ef8975c89ba8e0cbb4984016b662b8457dcb /julia.html.markdown
parentc8ad0d08093d692dc2d2d5edb1133f6c90318f42 (diff)
one more quick run over the code
Diffstat (limited to 'julia.html.markdown')
-rw-r--r--julia.html.markdown109
1 files changed, 51 insertions, 58 deletions
diff --git a/julia.html.markdown b/julia.html.markdown
index e5706062..71331818 100644
--- a/julia.html.markdown
+++ b/julia.html.markdown
@@ -30,7 +30,7 @@ This is based on Julia 1.0.0
3 # => 3 (Int64)
3.2 # => 3.2 (Float64)
2 + 1im # => 2 + 1im (Complex{Int64})
-2 // 3 # => 2//3 (Rational{Int64})
+2 // 3 # => 2 // 3 (Rational{Int64})
# All of the normal infix operators are available.
1 + 1 # => 2
@@ -81,29 +81,18 @@ false
2 < 3 < 2 # => false
# Strings are created with "
-try
- "This is a string."
-catch ; end
-
-# Julia has several types of strings, including ASCIIString and UTF8String.
-# More on this in the Types section.
+"This is a string."
# Character literals are written with '
-try
- 'a'
-catch ; end
+'a'
-# Some strings can be indexed like an array of characters
-try
- "This is a string"[1] # => 'T' # Julia indexes from 1
-catch ; end
-# However, this is will not work well for UTF8 strings,
-# so iterating over strings is recommended (map, for loops, etc).
+# Strings are UTF8 encoded. Only if they contain only ASCII characters can
+# they be safely indexed.
+ascii("This is a string")[1] # => 'T' # Julia indexes from 1
+# Otherwise, iterating over strings is recommended (map, for loops, etc).
# $ can be used for string interpolation:
-try
- "2 + 2 = $(2 + 2)" # => "2 + 2 = 4"
-catch ; end
+"2 + 2 = $(2 + 2)" # => "2 + 2 = 4"
# You can put any Julia expression inside the parentheses.
# Another way to format strings is the printf macro from the stdlib Printf.
@@ -157,19 +146,19 @@ SomeOtherVar123! = 6 # => 6
# functions are sometimes called mutating functions or in-place functions.
# Arrays store a sequence of values indexed by integers 1 through n:
-a = Int64[] # => 0-element Int64 Array
+a = Int64[] # => 0-element Int64 Array
# 1-dimensional array literals can be written with comma-separated values.
-b = [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
+b = [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-dimensional 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]
-# Arrays of a particular Type
-b = Int8[4, 5, 6] # => 3-element Int8 Array: [4, 5, 6]
+# Arrays of a particular type
+b = Int8[4, 5, 6] # => 3-element Int8 Array: [4, 5, 6]
# Add stuff to the end of a list with push! and append!
push!(a, 1) # => [1]
@@ -184,11 +173,11 @@ pop!(b) # => 6 and b is now [4,5]
# Let's put it back
push!(b, 6) # b is now [4,5,6] again.
-a[1] # => 1 # remember that Julia indexes from 1, not 0!
+a[1] # => 1 # remember that Julia indexes from 1, not 0!
# end is a shorthand for the last index. It can be used in any
# indexing expression
-a[end] # => 6
+a[end] # => 6
# we also have popfirst! and pushfirst!
popfirst!(a) # => 1 and a is now [2,4,3,4,5,6]
@@ -196,28 +185,30 @@ pushfirst!(a, 7) # => [7,2,4,3,4,5,6]
# 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]
sort(arr) # => [4,5,6]; arr is still [5,4,6]
sort!(arr) # => [4,5,6]; arr is now [4,5,6]
# Looking out of bounds is a BoundsError
try
- a[0] # => ERROR: BoundsError() in getindex at array.jl:270
- a[end + 1] # => ERROR: BoundsError() in getindex at array.jl:270
+ a[0]
+ # => BoundsError: attempt to access 7-element Array{Int64,1} at index [0]
+ a[end + 1]
+ # => BoundsError: attempt to access 7-element Array{Int64,1} at index [8]
catch e
println(e)
end
# 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.
+# library. You can look in the folder share/julia inside the julia folder to
+# find these files.
# You can initialize arrays from ranges
-a = [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.
-a[1:3] # => [1, 2, 3]
-a[2:end] # => [2, 3, 4, 5]
+a[1:3] # => [1, 2, 3]
+a[2:end] # => [2, 3, 4, 5]
# Remove elements from an array by index with splice!
arr = [3,4,5]
@@ -235,16 +226,16 @@ length(a) # => 8
# Tuples are immutable.
tup = (1, 2, 3) # => (1,2,3) # an (Int64,Int64,Int64) tuple.
-tup[1] # => 1
+tup[1] # => 1
try
tup[1] = 3 # => ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
catch e
println(e)
end
-# Many list functions also work on tuples
+# Many array functions also work on tuples
length(tup) # => 3
-tup[1:2] # => (1,2)
+tup[1:2] # => (1,2)
in(2, tup) # => true
# You can unpack tuples into variables
@@ -266,19 +257,20 @@ empty_dict = Dict() # => Dict{Any,Any}()
# You can create a dictionary using a literal
filled_dict = Dict("one" => 1, "two" => 2, "three" => 3)
-# => Dict{ASCIIString,Int64}
+# => Dict{String,Int64}
# Look up values with []
-filled_dict["one"] # => 1
+filled_dict["one"] # => 1
# Get all keys
keys(filled_dict)
-# => KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
+# => Base.KeySet for a Dict{String,Int64} with 3 entries. Keys:
+# "two", "one", "three"
# Note - dictionary keys are not sorted or in the order you inserted them.
# Get all values
values(filled_dict)
-# => ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
+# => Base.ValueIterator{Dict{String,Int64}} with 3 entries. Values: 2, 1, 3
# Note - Same as above regarding key ordering.
# Check for existence of keys in a dictionary with in, haskey
@@ -289,33 +281,33 @@ haskey(filled_dict, 1) # => false
# Trying to look up a non-existent key will raise an error
try
- filled_dict["four"] # => ERROR: key not found: four in getindex at dict.jl:489
+ filled_dict["four"] # => KeyError: key "four" not found
catch e
println(e)
end
# Use the get method to avoid that error by providing a default value
-# get(dictionary,key,default_value)
+# get(dictionary, key, default_value)
get(filled_dict, "one", 4) # => 1
get(filled_dict, "four", 4) # => 4
# Use Sets to represent collections of unordered, unique values
empty_set = Set() # => Set{Any}()
# Initialize a set with values
-filled_set = Set([1,2,2,3,4]) # => Set{Int64}(1,2,3,4)
+filled_set = Set([1, 2, 2, 3, 4]) # => Set([4, 2, 3, 1])
# Add more values to a set
-push!(filled_set, 5) # => Set{Int64}(5,4,2,3,1)
+push!(filled_set, 5) # => Set([4, 2, 3, 5, 1])
# Check if the values are in the set
in(2, filled_set) # => true
in(10, filled_set) # => false
# There are functions for set intersection, union, and difference.
-other_set = Set([3, 4, 5, 6]) # => Set{Int64}(6,4,5,3)
-intersect(filled_set, other_set) # => Set{Int64}(3,4,5)
-union(filled_set, other_set) # => Set{Int64}(1,2,3,4,5,6)
-setdiff(Set([1,2,3,4]), Set([2,3,5])) # => Set{Int64}(1,4)
+other_set = Set([3, 4, 5, 6]) # => Set([4, 3, 5, 6])
+intersect(filled_set, other_set) # => Set([4, 3, 5])
+union(filled_set, other_set) # => Set([4, 2, 3, 5, 6, 1])
+setdiff(Set([1,2,3,4]), Set([2,3,5])) # => Set([4, 1])
####################################################
@@ -356,8 +348,9 @@ end
# cat is a mammal
# mouse is a mammal
-for a in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
- println("$(a[1]) is a $(a[2])")
+for pair in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
+ from, to = pair
+ println("$from is a $to")
end
# prints:
# dog is a mammal
@@ -509,8 +502,8 @@ map(add_10, [1,2,3]) # => [11, 12, 13]
filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
# We can use list comprehensions for nicer maps
-[add_10(i) for i = [1, 2, 3]] # => [11, 12, 13]
-[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
+[add_10(i) for i = [1, 2, 3]] # => [11, 12, 13]
+[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
####################################################
## 5. Types
@@ -703,9 +696,9 @@ fight(Lion("RAR"), Lion("brown", "rarrr")) # => prints The lions come to a tie
# Under the hood
# You can take a look at the llvm and the assembly code generated.
-square_area(l) = l * l # square_area (generic function with 1 method)
+square_area(l) = l * l # square_area (generic function with 1 method)
-square_area(5) #25
+square_area(5) # => 25
# What happens when we feed square_area an integer?
code_native(square_area, (Int32,))