Test if string begins with number

New to Julia
1

Dear all,
it is possible to test whether a string starts with a number?
Let’s say I have the following:

julia> x="Some string"
"Some string"

julia> y="1 Another string"
"1 Another string"

julia> X=x[1]
'S': ASCII/Unicode U+0053 (category Lu: Letter, uppercase)

julia> Y=y[1]
'1': ASCII/Unicode U+0031 (category Nd: Number, decimal digit)

julia> parse(Int8, X)
ERROR: ArgumentError: invalid base 10 digit 'S'
Stacktrace:
 [1] #parse#330(::Int64, ::Function, ::Type{Int8}, ::Char) at ./parse.jl:43
 [2] parse(::Type{Int8}, ::Char) at ./parse.jl:38
 [3] top-level scope at none:0

julia> parse(Int8, Y)
1

How can I distinguish between X and Y and determine that Y is a number?
Thank you

2 
isdigit(X) && parse(Int8, X)

more generally, if you look for test functions, doing

julia> is\<tab>\<tab>

gives you a list of isX functions.

3

It is unclear if you want to check if a string starts with a number (ie something that would parse as a ::Real, or even broader, in Julia, eg "-12.7e9foo"), or simply a digit.

4

for the moment digit will do (thus the question is answered), but a more general approach might be handy in the future.

5

You have to be specific about how you want to generalize this; what would constitute valid strings, whether you need the number, etc. If you don’t, a regular expression can be used.

6

The more general approach you’re looking for is regex. Julia has regex functionality in Base, the relevant functions are listed here.

Be warned, regex notation is impossible to remember. :laughing:

7

regex notation is impossible to remember

Not anymore

8

To whoever it may concern, now the method startswith in the standard library accepts a regex as a prefix:

julia> startswith("1234 Hi!", r"\d+")
true

julia> startswith("1234 Hi!", r"\d")
true

julia> startswith("1234 Hi!", r"\w")
true

julia> startswith("1234 Hi!", r"[a-zA-Z]")
false

julia> startswith("1234 Hi!", r"[0-9]")
true