How to declare a string array for the purpose of concatenation

General Usage
1

Hi all,
I have the following code of converting a string array into a char array (MATLAB’s parlance)

This works

str1 = ["abc", "def", "ghi"]

function str_join(str2)
str=str2[1]

for i=2:1:length(str2)
    
    str = string(str,str2[i]) 
    
end

    return str

end 

str3 = str_join(str1)
display(str3)

Output: “abcdefghi”

This doesn’t work

str1 = ["abc", "def", "ghi"]

function str_join(str2)
str = Array{String}(undef,1)

str[1]=str2[1]

for i=2:1:length(str2)
    
    str = string(str,str2[i]) 
    
end

    return str

end 

str3 = str_join(str1)
display(str3)

Output: “["abc"]defghi”

Is there any way to get rid of this residue of undef?

2

The undef isn’t really relevant here. The point is that you’re doing string(str, ...), where str is an array of strings (initially with one element).

string(["abc"]) gives ["abc"], which just isn’t what you want here.

If you want the easy answer, the way to join strings is…join() :slightly_smiling_face:

julia> str1 = ["abc", "def", "ghi"]
3-element Vector{String}:
 "abc"
 "def"
 "ghi"

julia> join(str1)
"abcdefghi"
5 Likes
3

Thank you rdeits for your input. I was used to this MATLAB’s way

str1 = ["abc", "def", "ghi"];
str2 = [];

for i=1:1:length(str1)
    
    str2 = [str2 str1(i)] ;
    
end
4

https://docs.julialang.org/en/v1/manual/strings/#Common-Operations

might want to give the short and sweet Manual a read.

2 Likes
5

Thank you jling for the link. Now going through it more carefully!

6

FWIW, prod(str1) produces here the same result as join(str1)

1 Like
7

Thank you Rafael.

8

Adding to this, join lets you specify a delimiter:

julia> join(("a","b","c"), "; ")
"a; b; c"
1 Like
9

Interesting. Thank you Gustaphe.

10

Another cool use of join is you don’t need to create the string if you’re printing it to a file or other io:

julia> join(stdout, ("a", "b", "c"), "; ")
a; b; c
julia> open("file.txt", "w") do f
           join(f, ("a", "b", "c"), "; ")
       end
3 Likes