I have a request that I make in an API using GET
LWP::UserAgent,
the data is returned as JSON, with up to two results at most as follows:
{
"status":1,
"time":1507891855,
"response":{
"prices":{
"nome1\u2122":{
"preco1":1111,
"preco2":1585,
"preco3":1099
},
"nome2":{
"preco1":519,
"preco2":731,
"preco3":491
}
}
}
}
Dump:
$VAR1 = {
'status' => 1,
'time' => 1507891855,
'response' => {
'prices' => {
'nome1' => {
'preco1' => 1111,
'preco3' => 1099,
'preco2' => 1585
},
'nome2' => {
'preco3' => 491,
'preco1' => 519,
'preco2' => 731
}
}
}
};
What I would like to do is:
Take this data and save it in a variable to make a comparison using if with another variable that already has the name stored. The comparison would be with name1 / name2 and if it is true with the other variable it would get preco2 and preco3 to print everything
My biggest problem in the case is that some of these names in JSON contain characters like (TradeMark) that comes as \u2122 (some cases are other characters), so I can not make the comparison with the name of the other variable that is already with the correct name
nome1™
If I could only save the JSON already "converted" the characters would help me with the rest.
Basically after doing the request for the API I want to save the contents in a variable already converting all \u2122 to their respective character (this is the part that I do not know how to do in Perl) and then using another variable to compare them names are equal to show the price
Thanks for the help and any questions please tell me that I try to explain again in another way.
If I understand correctly, you need to get the JSON that you receive in UTF8 format to an internal variable that you can process. For that, you may use JSON::XS:
use utf8;
use JSON::XS;
my $name = "nome1™";
my $var1 = decode_json $utf8_encoded_json_text;
# Compare with name in $name
if( defined $var1->{'response'}->{'prices'}->{$name} ) {
# Do something with the name that matches
my $match = $var1->{'response'}->{'prices'}->{$name};
print $match->{'preco1'}, "\n";
}
Make sure you tell the Perl interpreter that your source is in UTF8 by specifying use utf8; at the beginning of the script. Then make sure you are editing the script with an editor that supports that format.
The function decode_json will return a ref to the converted value. In this case a hash ref. From there you work your way into the JSON.
If you know $name is going to be in the JSON you may omit the defined part. Otherwise, the defined clause will tell you whether the hash value is there. One you know, you may do something with it. If the hash values are a single word with no special characters, you may use $var1->{response}->{prices}->{$name}, but it is always safer to use $var1->{'response'}->{'prices'}->{$name}. Perl gets a bit ugly handling hash refs...
By the way, in JSON::XS you will also find the encode_json function to do the opposite and also an object oriented interface.
Related
So I have a JSON file of a somewhat known format { String => JSON::Type, ... }. So it is basically of type Hash(String, JSON::Type). But when I try and read it from file to memory like so: JSON.parse(File.read(#cache_file)).as(Hash(String, JSON::Type)) I always get an exception: can't cast JSON::Any to Hash(String, JSON::Type)
I'm not sure how I am supposed to handle the data if I can't cast it.
What I basically want to do is the following:
save JSON::Type data under a String key
replace JSON::Type data with other JSON::Type data under a String key
And of course read from / write to file...
Here's the whole thing I've got so far:
class Cache
def initialize(#cache_file = "/tmp/cache_file.tmp")
end
def cache(cache_key : (String | Symbol))
mutable_cache_data = data
value = mutable_cache_data[cache_key.to_s] ||= yield.as(JSON::Type)
File.write #cache_file, mutable_cache_data
value
end
def clear
File.delete #cache_file
end
def data
unless File.exists? #cache_file
File.write #cache_file, {} of String => JSON::Type
end
JSON.parse(File.read(#cache_file)).as(Hash(String, JSON::Type))
end
end
puts Cache.new.cache(:something) { 10 } # => 10
puts Cache.new.cache(:something) { 'a' } # => 10
TL;DR I want to read a JSON file into a Hash(String => i_dont_care), replace a value under a given key name and serialize it to file again. How do I do that?
JSON.parse returns an JSON::Any, not a Hash so you can't cast it. You can however access the underlying raw value as JSON.parse(file).raw and cast this as hash.
Then your code is basically working (I've fixed a few error): https://carc.in/#/r/28c1
You can use use Hash(String, JSON::Type).from_json(File.read(#cache_file)). Hopefully you can restrict the type of JSON::Type down to something more sensible too. JSON::Any and JSON.parse_raw are very much a last resort compared to simply representing your schema using Hash, Array and custom types using JSON.mapping.
I'm parsing a JSON string that is stored in a database.
{"name":"simon", "age":"23", "height":"tall"}
I'm pulling the data, then decoding. When running the code below, I'm receiving weird 'HASH' values back.
use JSON;
$data = decode_json($row->{'address'});
for my $key (keys %$data){
if($data->{$key} ne ''){
$XML .= " <$key>$data->{$key}</$key>";
}
}
// Returns data like so
<company_type>HASH(0x27dbac0)</company_type>
<county>HASH(0x27db7c0)</county>
<address1>HASH(0x27dba90)</address1>
<company_name>HASH(0x27db808)</company_name>
The Error happens when I have a data set like so:
{"name":"", "age":{}, "height":{}}
I don't understand why JSON / Arrays / Hashes have to be so difficult to work with in Perl. What point am I missing?
You are processing a flat hash, while your data in fact has another, nested, hashref. In the line
{ "name":"", "age":{}, "height":{} }
the {} may be intended to mean "nothing" but are in fact JSON "object", the next level of nested data (which are indeed empty). In Perl we get a hashref for it and that's what your code prints.
The other pillar of JSON is an "array" and in Perl we get an arrayref. And that's that -- decode_json gives us back the top-level hashref, which when dereferenced into a hash may contain further hash or array references as values. If you print the whole structure with Data::Dumper you'll see that.
To negotiate this we have to test each time for a reference. Since a dereferenced hash or array may contain yet further levels (more references), we need to use either a recursive routine (see this post for an example) or a module for complex data structures. But for the first level
for my $key (keys %$data)
{
next if $data->{$key} eq '';
my $ref_type = ref $data->{$key};
# if $data->{key} is not a reference ref() returns an empty string (false)
if (not $ref_type) {
$XML .= " <$key>$data->{$key}</$key>";
}
elsif ($ref_type eq 'HASH') {
# hashref, unpack and parse. it may contain references
say "$_ => $data->{$key}{$_}" for keys %{ $data->{$key} };
}
elsif ($ref_type eq 'ARRAY') {
# arrayref, unpack and parse. it may contain references
say "#{$data->{$key}}";
}
else { say "Reference is to type: $ref_type" }
}
If the argument of ref is not a reference (but a string or a number) ref returns an empty string, which evaluates as false, which is when you have plain data. Otherwise it returns the type the reference is to. Coming from JSON it can be either a HASH or an ARRAY. This is how nesting is accomplished.
In the shown example you are runnig into hashref. Since the ones you show are empty you can just discard them and the code for the specific example can reduce greatly, to one statement. However, I'd leave the other tests in place. This should also work as it stands with the posted example.
I am confused about accessing the contents of some JSON data that I have decoded. Here is an example
I don't understand why this solution works and my own does not. My questions are rephrased below
my $json_raw = getJSON();
my $content = decode_json($json_raw);
print Data::Dumper($content);
At this point my JSON data has been transformed into this
$VAR1 = { 'items' => [ 1, 2, 3, 4 ] };
My guess tells me that, once decoded, the object will be a hash with one element that has the key items and an array reference as the value.
$content{'items'}[0]
where $content{'items'} would obtain the array reference, and the outer $...[0] would access the first element in the array and interpret it as a scalar. However this does not work. I get an error message use of uninitialized value [...]
However, the following does work:
$content->{items}[0]
where $content->{items} yields the array reference and [0] accesses the first element of that array.
Questions
Why does $content{'items'} not return an array reference? I even tried #{content{'items'}}, thinking that, once I got the value from content{'items'}, it would need to be interpreted as an array. But still, I receive the uninitialized array reference.
How can I access the array reference without using the arrow operator?
Beginner's answer to beginner :) Sure not as profesional as should be, but maybe helps you.
use strict; #use this all times
use warnings; #this too - helps a lot!
use JSON;
my $json_str = ' { "items" : [ 1, 2, 3, 4 ] } ';
my $content = decode_json($json_str);
You wrote:
My guess tells me that, once decoded, the object will be a hash with
one element that has the key items and an array reference as the value.
Yes, it is a hash, but the the decode_json returns a reference, in this case, the reference to hash. (from the docs)
expects an UTF-8 (binary) string and tries to parse that
as an UTF-8 encoded JSON text,
returning the resulting reference.
In the line
my $content = decode_json($json_str);
you assigning to an SCALAR variable (not to hash).
Because you know: it is a reference, you can do the next:
printf "reftype:%s\n", ref($content);
#print: reftype:HASH ^
#therefore the +------- is a SCALAR value containing a reference to hash
It is a hashref - you can dump all keys
print "key: $_\n" for keys %{$content}; #or in short %$content
#prints: key: items
also you can assing the value of the "items" (arrayref) to an scalar variable
my $aref = $content->{items}; #$hashref->{key}
#or
#my $aref = ${$content}{items}; #$hash{key}
but NOT
#my $aref = $content{items}; #throws error if "use strict;"
#Global symbol "%content" requires explicit package name at script.pl line 20.
The $content{item} is requesting a value from the hash %content and you never defined/assigned such variable. the $content is an scalar variable not hash variable %content.
{
#in perl 5.20 you can also
use 5.020;
use experimental 'postderef';
print "key-postderef: $_\n" for keys $content->%*;
}
Now step deeper - to the arrayref - again you can print out the reference type
printf "reftype:%s\n", ref($aref);
#reftype:ARRAY
print all elements of array
print "arr-item: $_\n" for #{$aref};
but again NOT
#print "$_\n" for #aref;
#dies: Global symbol "#aref" requires explicit package name at script.pl line 37.
{
#in perl 5.20 you can also
use 5.020;
use experimental 'postderef';
print "aref-postderef: $_\n" for $aref->#*;
}
Here is an simple rule:
my #arr; #array variable
my $arr_ref = \#arr; #scalar - containing a reference to #arr
#{$arr_ref} is the same as #arr
^^^^^^^^^^ - array reference in curly brackets
If you have an $arrayref - use the #{$array_ref} everywhere you want use the array.
my %hash; #hash variable
my $hash_ref = \%hash; #scalar - containing a reference to %hash
%{$hash_ref} is the same as %hash
^^^^^^^^^^^ - hash reference in curly brackets
If you have an $hash_ref - use the %{$hash_ref} everywhere you want use the hash.
For the whole structure, the following
say $content->{items}->[0];
say $content->{items}[0];
say ${$content}{items}->[0];
say ${$content}{items}[0];
say ${$content->{items}}[0];
say ${${$content}{items}}[0];
prints the same value 1.
$content is a hash reference, so you always need to use an arrow to access its contents. $content{items} would refer to a %content hash, which you don't have. That's where you're getting that "use of uninitialized value" error from.
I actually asked a similar question here
The answer:
In Perl, a function can only really return a scalar or a list.
Since hashes can be initialized or assigned from lists (e.g. %foo = (a => 1, b => 2)), I guess you're asking why json_decode returns something like { a => 1, b => 2 } (a reference to an anonymous hash) rather than (a => 1, b => 2) (a list that can be copied into a hash).
I can think of a few good reasons for this:
in Perl, an array or hash always contains scalars. So in something like { "a": { "b": 3 } }, the { "b": 3 } part has to be a scalar; and for consistency, it makes sense for the whole thing to be a scalar in the same way.
if the hash is quite large (many keys at top-level), it's pointless and expensive to iterate over all the elements to convert it into a list, and then build a new hash from that list.
in JSON, the top-level element can be either an object (= Perl hash) or an array (= Perl array). If json_decode returned a list in the former case, it's not clear what it would return in the latter case. After decoding the JSON string, how could you examine the result to know what to do with it? (And it wouldn't be safe to write %foo = json_decode(...) unless you already knew that you had a hash.) So json_decode's behavior works better for any general-purpose library code that has to use it without already knowing very much about the data it's working with.
I have to wonder exactly what you passed as an array to json_decode, because my results differ from yours.
#!/usr/bin/perl
use JSON qw (decode_json);
use Data::Dumper;
my $json = '["1", "2", "3", "4"]';
my $fromJSON = decode_json($json);
print Dumper($fromJSON);
The result is $VAR1 = [ '1', '2', '3', '4' ];
Which is an array ref, where your result is a hash ref
So did you pass in a hash with element items which was a reference to an array?
In my example you would get the array by doing
my #array = #{ $fromJSON };
In yours
my #array = #{ $content->{'items'} }
I don't understand why you dislike the arrow operator so much!
The decode_json function from the JSON module will always return a data reference.
Suppose you have a Perl program like this
use strict;
use warnings;
use JSON;
my $json_data = '{ "items": [ 1, 2, 3, 4 ] }';
my $content = decode_json($json_data);
use Data::Dump;
dd $content;
which outputs this text
{ items => [1 .. 4] }
showing that $content is a hash reference. Then you can access the array reference, as you found, with
dd $content->{items};
which shows
[1 .. 4]
and you can print the first element of the array by writing
print $content->{items}[0], "\n";
which, again as you have found, shows just
1
which is the first element of the array.
As #cjm mentions in a comment, it is imperative that you use strict and use warnings at the start of every Perl program. If you had those in place in the program where you tried to access $content{items}, your program would have failed to compile, and you would have seen the message
Global symbol "%content" requires explicit package name
which is a (poorly-phrased) way of telling you that there is no %content so there can be no items element.
The scalar variable $content is completely independent from the hash variable %content, which you are trying to access when you write $content{items}. %content has never been mentioned before and it is empty, so there is no items element. If you had tried #{$content->{items}} then it would have worked, as would #{${$content}{items}}
If you really have a problem with the arrow operator, then you could write
print ${$content}{items}[0], "\n";
which produces the same output; but I don't understand what is wrong with the original version.
I'm trying to construct json text as show below. But the variables such as $token, $state, $failedServers are not been replaced with its value. Note- I don't want to use any module specifically for this to work, I just want some plain string to work. Can anyone help me ?
my $json = '{"serverToken":"$token", "state":"$state","parameters" :"$failedServers"}';
current output was:
{"serverToken":"$token", "state":"$state","parameters" :"$failedServers"}
needed output format:
{"serverToken":"1213", "state":"failed","parameters" :"oracleapps.veeralab.com,suntrust.com"}
Your variables are not being replaced, because they are inside of a single-quoted string--that is, they are inside a string quoted by ' characters. This prevents variable substitution.
You will also be much better off creating JSON using a JSON library, such as this one. Simply using a quoted string is very dangerous. Suppose your one of your variables ends up containing a special character; you will end up with invalid JSON.
{"serverToken":"123"ABC", "state":"offline", "paramameters":"bugs"}
If your variables come from user input, really bad things could happen. Imagine that $token is set to equal foo", "state":"online", "foo":"bar. Your resulting JSON structure would be:
{"serverToken":"foo", "state":"online", "foo":"bar", "state":"offline" ...
Certainly not what you want.
Possible solutions:
The most blatantly obvious solution is simply not to the ' quote character. This has the drawback of requiring you to escape your double quote (") characters, though, but it's easy:
my $json = "{\"serverToken\":\"$token\", \"state\":\"$state\",\"parameters\" :\"$failedServers\"}";
Another option is to use sprintf:
my $json = sprintf('{"serverToken":"%s", "state":"%s", "parameters":"%s"}', $token, $state, $failedServers);
But by far, the best solution, because it won't break with wonky input, is to use a library:
use JSON;
my $json = encode_json( {
serverToken => $token,
state => $state,
paramaters => $failedServers
} );
Given an arbitrarily nested data structure, how can I create a new data structure so that all the elements in it have been standardized by applying a function on all the elements depending on the type of the element. For example, I might have
$data = {
name => 'some one',
date => '2010-10-10 12:23:45',
sale => [34, 22, 65],
cust => {
name => 'Jimmy',
addr => '1 Foobar Way',
amnt => 452.024,
item => ['books', 'pens', 'post-it notes']
}
}
and I want to convert all text values to upper case, all dates to UTC date times, find the square of all integers, round down all real numbers and add 1, and so on. So, in effect, I want to apply a different function to each element depending on the type of element.
In reality the data might arrive via a database query, in which case they are already a Perl data structure, or they might start life as a JSON object, in which case I can use JSON::from_json to convert it to a Perl data structure. The idea is to standardize all the values in the data structure based on the value type, and then spit out the Perl data structure back again as a JSON object.
I read the answers to executing a function on every element of a data structure and feel that Data::Rmap might do the trick, but can't figure out how. Seems like Rmap works on all the keys as well, not just the values.
It's crazy straightforward with Data::Rmap you mentioned.
use Data::Rmap qw( rmap );
rmap { $_ = transform($_); } $data;
Regarding the question in the comments:
use Data::Rmap qw( rmap );
use Scalar::Util qw( looks_like_number );
# Transforms $_ in place.
sub transform {
if (looks_like_number($_)) {
if (...) {
$_ *= 2;
}
$_ = 0+$_; # Makes it look like a number to JSON::XS
} else {
...
}
}
&rmap(\&transform, $data);