Julia array / list comprehension and generator expression examples

julia_comprehension_generator_examples.txt

julia> VERSION
v"1.3.0"

julia> # Julia documention on array) comprehensions and generator expressions:
julia> # https://docs.julialang.org/en/v1/manual/arrays/#Comprehensions-1
julia> # https://docs.julialang.org/en/v1/manual/arrays/#Generator-Expressions-1

julia> # The code below uses generator expressions
julia> # Double list comprehension for the first fifty-one terms of the power series of the exponential function
julia> sum(prod(1/i for i in 1:n) for n in 1:50) + 1
2.7182818284590455

julia> # As a function (function assignment form)
julia> f(x) = sum(prod(x/i for i in 1:n) for n in 1:50) + 1
f (generic function with 1 method)

julia> f(1)
2.7182818284590455

julia> # Accuracy of the approximation
julia> f(15) - exp(15)
-8.638016879558563e-7

julia> # Nested list comprehension with conditional
julia> prod(i^2 for n in 1:10 for i in 1:n if i % 3 == 1)
154747698518425600

julia> # Using '=' instead of 'in'; this is identical
julia> prod(i^2 for n = 1:10 for i = 1:n if i % 3 == 1)
154747698518425600

julia> # Two-dimensional list comprehension
julia> [x * y for x in 2:2:10, y in 10:10:50]
5×5 Array{Int64,2}:
  20   40   60   80  100
  40   80  120  160  200
  60  120  180  240  300
  80  160  240  320  400
 100  200  300  400  500

julia> # With a conditional, thus reduces to a one-dimensional array
julia> [x * y for x in 2:2:10, y in 10:10:50 if 3x > y]
6-element Array{Int64,1}:
  40
  60
  80
 100
 160
 200