I'm not a programmer, but I find myself writing some simple ruby and aren't sure about a few things.
I have the following function
def resolve_name(ns_name)
ip = Resolv.getaddress(ns_name)
return ip
end
and the array
array = ['ns-1.me.com', 'ns-2.me.com']
What I want to do is to pass every element in the array to the function to be evaluated, and spit out to... something. Probably a variable. Once I have the resolved IPs I'll be passing them to an erb template. Not quite sure yet how to handle when there may be 1 to 4 possible results either.
What I want think I need to do is do an each.do and typecast to string into my function, but I haven't been able to figure out how to actually do that or phrase my problem properly for google to tell me.
http://ruby-doc.org/core-2.0.0/doc/syntax/calling_methods_rdoc.html#label-Array+to+Arguments+Conversion Doesn't quite have what I'm looking for.
irb(main):010:0> resolved = resolve_name(array)
TypeError: no implicit conversion of Array into String
Any suggestions?
Take a look at the documentation for ruby's Enumerable, which arrays implement. What you're looking for is the map method, which takes each element of an enumerable (i.e. an array) and passes it to a block, returning a new array with the results of the blocks. Like this:
array.map{|element| resolve_name(element) }
As an aside, in your method, you do not need to use a local variable if all you're doing with it is returning its value; and the return statement is optional - ruby methods always return the result of the last executed statement. So your method could be shortened to this:
def resolve_name(ns_name)
Resolv.getaddress(ns_name)
end
and then you really all it's doing is wrapping a method call in another. So ultimately, you can just do this (with array renamed to ns_names to make it self-explanatory):
ns_names = ['ns-1.me.com', 'ns-2.me.com']
ip_addresses = ns_names.map{|name| Resolv.getaddress(name) }
Now ip_addresses is an array of IP addresses that you can use in your template.
If you pass an array you could do:
def resolve_name(ns_name)
res = []
ns_name.each do |n|
res << {name: n, ip: Resolv.getaddress(name) }
end
res
end
And get an array of hashes so you know which address has which ip
Related
Is there a way to remove a number from an attibute array in an update? For example, if I want to update all of an alchy's booze stashes if he runs out of a particular type of booze:
Alchy has_many :stashes
Stash.available_booze_types = [] (filled with booze.ids)
Booze is also a class
#booze.id = 7
if #booze.is_all_gone
#alchy.stashes.update(available_booze_types: "remove #booze.id")
end
update: #booze.id may or may not be present in the available_booze_types array
... so if #booze.id was in any of the Alchy.stash instances (in the available_booze_types attribute array), it would be removed.
I think you can do what you want in the following way:
if #booze.is_all_gone
#alchy.stashes.each do |stash|
stash.available_booze_types.delete(#booze.id)
end
end
However, it looks to me like there are better ways to do what you are trying to do. Rails gives you something like that array by using relations. Also, the data in the array will be lost if you reset the app (if as I understand available_booze_types is an attribute which is not stored in a database). If your application is correctly set up (an stash has many boozes), an scope like the following in Stash class seems to me like the correct approach:
scope :available_boozes, -> { joins(:boozes).where("number > ?", 0) }
You can use it in the following way:
#alchy.stashes.available_boozes
which would only return the ones that are available.
In the Hash documentation, the section on Object keys seems to imply that you can use any type as a Hash key as long as you indicate but I am having trouble when trying to use an array as the key:
> my %h{Array};
{}
> %h{[1,2]} = [3,4];
Type check failed in binding to parameter 'key'; expected Array but got Int (1)
in block <unit> at <unknown file> line 1
Is it possible to do this?
The [1,2] inside the %h{[1,2]} = [3,4] is interpreted as a slice. So it tries to assign %h{1} and %{2}. And since the key must be an Array, that does not typecheck well. Which is what the error message is telling you.
If you itemize the array, it "does" work:
my %h{Array};
%h{ $[1,2] } = [3,4];
say %h.perl; # (my Any %{Array} = ([1, 2]) => $[3, 4])
However, that probably does not get what you want, because:
say %h{ $[1,2] }; # (Any)
That's because object hashes use the value of the .WHICH method as the key in the underlying array.
say [1,2].WHICH; say [1,2].WHICH;
# Array|140324137953800
# Array|140324137962312
Note that the .WHICH values for those seemingly identical arrays are different.
That's because Arrays are mutable. As Lists can be, so that's not really going to work.
So what are you trying to achieve? If the order of the values in the array is not important, you can probably use Sets as keys:
say [1,2].Set.WHICH; say [1,2].Set.WHICH
# Set|AEA2F4CA275C3FE01D5709F416F895F283302FA2
# Set|AEA2F4CA275C3FE01D5709F416F895F283302FA2
Note that these two .WHICHes are the same. So you could maybe write this as:
my %h{Set};
dd %h{ (1,2).Set } = (3,4); # $(3, 4)
dd %h; # (my Any %{Set} = ((2,1).Set) => $(3, 4))
Hope this clarifies things. More info at: https://docs.raku.org/routine/WHICH
If you are really only interested in use of an Object Hash for some reason, refer to Liz's answer here and especially the answers to, and comments on, a similar earlier question.
The (final1) focus of this answer is a simple way to use an Array like [1,'abc',[3/4,Mu,["more",5e6],9.9],"It's {<sunny rainy>.pick} today"] as a regular string hash key.
The basic principle is use of .perl to approximate an immutable "value type" array until such time as there is a canonical immutable Positional type with a more robust value type .WHICH.
A simple way to use an array as a hash key
my %hash;
%hash{ [1,2,3].perl } = 'foo';
say %hash{ [1,2,3].perl }; # displays 'foo'
.perl converts its argument to a string of Perl 6 code that's a literal version of that argument.
say [1,2,3].perl; # displays '[1, 2, 3]'
Note how spaces have been added but that doesn't matter.
This isn't a perfect solution. You'll obviously get broken results if you mutate the array between key accesses. Less obviously you'll get broken results corresponding to any limitations or bugs in .perl:
say [my %foo{Array},42].perl; # displays '[(my Any %{Array}), 42]'
1 This is, hopefully, the end of my final final answer to your question. See my earlier 10th (!!) version of this answer for discussion of the alternative of using prefix ~ to achieve a more limited but similar effect and/or to try make some sense of my exchange with Liz in the comments below.
Scala beginner who is trying to store values obtains in a Scala foreach loop but failing miserably.
The basic foreach loop looks like this currently:
order.orderList.foreach((x: OrderRef) => {
val references = x.ref}))
When run this foreach loop will execute twice and return a reference each time. I'm trying to capture the reference value it returns on each run (so two references in either a list or array form so I can access these values later)
I'm really confused about how to go about doing this...
I attempted to retrieve and store the values as an array but when ran, the array list doesn't seem to hold any values.
This was my attempt:
val newArray = Array(order.orderList.foreach((x: OrderRef) => {
val references = x.ref
}))
println(newArray)
Any advice would be much appreciated. If there is a better way to achieve this, please share. Thanks
Use map instead of foreach
order.orderList.map((x: OrderRef) => {x.ref}))
Also val references = x.ref doesn't return anything. It create new local variable and assign value to it.
Agree with answer 1, and I believe the reason is below:
Return of 'foreach' or 'for' should be 'Unit', and 'map' is an with an changed type result like example below:
def map[B](f: (A) ⇒ B): Array[B]
Compare To for and foreach, the prototype should be like this
def foreach(f: (A) ⇒ Unit): Unit
So If you wanna to get an changed data which is maped from your source data, considering more about functions like map, flatMap, and these functions will traverse all datas like for and foreach(except with yield), but with return values.
Edit: I did try using fetch()
I seem to have break something in Julia this week. I had played with the SharedArray type on a computer with 12 threads (6 doble thread cpu), I maneged to get a result and to print it and save it as matrix text file without problem, more or less following the instructions on http://docs.julialang.org/en/release-0.4/manual/parallel-computing/#shared-arrays. I had this routine where I initialized a number of workers and an Array, pass them as argument to a function, and expected to obtain a SharedArray with numerical values in return. It went more or less like this
addprocs(11)
BCero=rand(128,128)
ConjuntoX=Array[]
for j,k=1:128
push!(ConjuntoX, [j,k])
end
function obtenerKernelParalell(LasB::Array, lasX::Array, jmax::Int)
result=SharedArray(Float64,(jmax,jmax))
#sync #parallel for j=1:jmax
xj=lasX[j]
for k=1:j
xk=lasX[k]
for l=1:jmax
xl=lasX[l]
result[j,k]+= LasB[(xk-xl+xconstante)...]*LasB[(xj-xl+xconstante)...]
end
end
end
end
KSuaveParalel=obtenerKernelParalell(BceroSuave, ConjuntoX,128);
What I did get after runing this for the first time was an array that behaved itself like a normal Array. If I typed KSuaveParalel[3,12] I obtained a value. But now I get the next thing from the REPL:
KSuaveParalel
11-element Array{Any,1}:
RemoteRef{Channel{Any}}(2,1,122)
RemoteRef{Channel{Any}}(3,1,123)
RemoteRef{Channel{Any}}(4,1,124)
RemoteRef{Channel{Any}}(5,1,125)
RemoteRef{Channel{Any}}(6,1,126)
RemoteRef{Channel{Any}}(7,1,127)
RemoteRef{Channel{Any}}(8,1,128)
RemoteRef{Channel{Any}}(9,1,129)
RemoteRef{Channel{Any}}(10,1,130)
RemoteRef{Channel{Any}}(11,1,131)
RemoteRef{Channel{Any}}(12,1,132)
So I got an array of References... and I do not know how to get its values. Also using fetch() doesn't seem to work.
What is going on here?
Edit:
You need to make sure you return the array in the function.
i.e. return result
You will want to call fetch() on each Remote Reference object to wait and get the value that will be returned.
[fetch(x) for x in KSuaveParalel]
The RemoteRef object is returned immediately (i.e. before the computation has actually been done). See this answer (Julia Parallel macro does not seem to work) and the docs for more info.
http://docs.julialang.org/en/release-0.4/stdlib/parallel/#Base.fetch
Okey, sort of figured a way to do it, but is not probably the most efficient way to do it: If I convert INSIDE the function the result from SharredArray to Array, I get the (apparently) correct result:
function obtenerKernelParalell(LasB::Array, lasX::Array, jmax::Int)
result=SharedArray(Float64,(jmax,jmax))
#sync #parallel for j=1:jmax
xj=lasX[j]
for k=1:j
xk=lasX[k]
for l=1:jmax
xl=lasX[l]
result[j,k]+= LasB[(xk-xl+xconstante)...]*LasB[(xjxl+xconstante)...]
end
end
end
result=Array(result)
return result
end
Is this because the conversion does the fetch() with the right settings automatically?
I'm new to Perl, and this thing has got me stuck for far too long...
I want to dump a readable representation of the object itself from inside a function (I'm trying to debug something, and I'm doing this by returning an array reference which the caller expects, but containing an object dump rather than human readable text as per normal) so in my package I have:
use Data::Dumper;
sub somefunctionName{
my $self = shift;
my $d = Dumper($self);
my #retval = ();
push(#retval, $d);
return \#retval;
}
This is giving me the error "Can't use string ("the literal object dump goes here") as a HASH ref while "strict refs" in use"
I can't for the life of me figure out a way to make the error go away, no matter how I mess with the backslashes, and what I've done above looks to me like exactly what every online tutorial does... But I'm obviously missing the point somewhere.
What am I doing wrong?
According to the documentation
Dumper(LIST)
Returns the stringified form of the values in the list, subject to the configuration options below. The values will be named $VAR n in the output, where n is a numeric suffix. Will return a list of strings in a list context.
You should be able to do
#retval = Dumper($self);
return \#retval