CODEWITHSUNDEEP
pythonnumpyjulia
tlnagy
tlnagy

Reputation: 3474

Convert array of ints to array of characters and vice versa in Julia

In Python/NumPy, I can convert arrays of ints to arrays of characters quite easily. How can I do this in Julia?

For example in Python:

In [6]: np.array(["A", "T", "C"]).view(np.int32)
Out[6]: array([65, 84, 67], dtype=int32)

And vice versa

In [15]: np.array([65, 84, 67]).view("S8")
Out[15]:
array([b'A', b'T', b'C'],
      dtype='|S8')

Upvotes: 1

Views: 774

Answers (3)

amrods
amrods

Reputation: 2131

use Char and Int:

Char(120) # = 'x'
Int('x') # = 120

A more complete answer:

ints = [65, 84, 67]
chars = map(Char, ints)

and

chars = ['A', 'T', 'C']
ints = map(Int, chars)

notice that characters and strings are of different types in Julia, see http://docs.julialang.org/en/latest/manual/strings/#characters

EDIT: You can also use the constructors Char and Int:

Char[65, 84, 67]
Int['A', 'T', 'C']

Upvotes: 2

Dan Getz
Dan Getz

Reputation: 18217

For a more instantaneous conversion, you can use ASCIIStrings and UInt8 arrays. Chars take four bytes of memory and don't use the compact one byte representation. The code will be:

# chars in s1 to ints in v1
s1 = ASCIIString("ATC")
v1 = s.data

# ints in v2 to chars in s2
v2 = UInt8[65,66,67]
s2 = ASCIIString(v)

In both cases, the same memory is backing both variables, meaning the operation is "instantaneous" but changing one variable would change the other.

Upvotes: 1

Warren Weckesser
Warren Weckesser

Reputation: 114781

Take a look at reinterpret:

julia> a = ['A' 'T' 'C']
1x3 Array{Char,2}:
 'A'  'T'  'C'

julia> b = reinterpret(Int32, a)
1x3 Array{Int32,2}:
 65  84  67

That makes a and b view the same memory, like a numpy "view". For example, if I change an element of a:

julia> a[1] = 'Z'
'Z'

b is also changed:

julia> b
1x3 Array{Int32,2}:
 90  84  67

Upvotes: 4

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