How to fill list with JSON data?
Here's my code:
my $groups = get_groups($t);
my #group;
my $i = 0;
do {
push(#group, {
groups => [
{ type => $groups->{groups}->[$i]->{type} , group => $groups->{groups}->[$i]->{group} },
]
});
$i++;
} while ($i < length $groups->{groups});
Here is the json sample:
{
"error":false,
"message":"success",
"group":[
{"type":1,"group":"group1"},
{"type":2,"group":"group2"},
{"type":3,"group":"group3"},
{"type":4,"group":"group4"},
{"type":5,"group":"group5"}
]
}
Function get_groups($t); will return above json. I want to get the array group and put it into list groups. But I got:
Can't use string ("0") as a HASH ref while "strict refs" in use
From the documentation of length:
Returns the length in characters of the value of EXPR. If EXPR is
omitted, returns the length of $_ . If EXPR is undefined, returns
undef.
This function cannot be used on an entire array or hash to find out
how many elements these have. For that, use scalar #array and scalar
keys %hash , respectively.
To get the number of elements in an array reference, you need to dereference it and put it into scalar context.
my $foo = [ qw/a b c/ ];
my $number_of_elements = scalar #{ $foo }; # 3
What you actually want to do is loop over every team in the teams array. No need to get the number of elements.
my #teams;
foreach my $team ( #{ $opsteams->{teams} } ) {
push #teams, {
type => $team->{type},
team => $team->{team},
};
}
There are some extra layers of depth in your code. I'm not sure what they are for. It actually looks like you just want the teams in #teams, which really would be
my #teams = #{ $opsteams->{teams} };
Related
I building an array from an other.
I have the keys and the values but I don't know how deep can be my new array
I was using the eval function but SONAR refuses it. So I have to find an other way.
$splitpair[0] = array("key1", "key2", "...", "keyN");
$splitpair[1] = "val1";
$returnArray[$splitpair[0]] = $splitpair[1];
I want my returned array like this: $returnArray[key1][key2][...][keyN] = "val1";
you can iterate over your indexes and move a reference to point to the last nested array
`
$returnArray = [];
$buffer = &$returnArray;//buffer points to $returnArray
$array = array('key1','key2','key3');
foreach($array as $index){
if(!(isset($buffer[$index])&&is_array($buffer[$index]))){
$buffer[$index]=[]; //if $buffer[$index] is not an array, initialize it
}
$buffer=&$buffer[$index];//buffer points to the last nested array ($returnArray['key1']['key2']....[$index])
}
$buffer='val1';
var_dump($returnArray);
`
I'm trying to use a PCRE regular expression to extract some JSON. I'm using a version of MariaDB which does not have JSON functions but does have REGEX functions.
My string is:
{"device_types":["smartphone"],"isps":["a","B"],"network_types":[],"countries":[],"category":["Jebb","Bush"],"carriers":[],"exclude_carriers":[]}
I want to grab the contents of category. I'd like a matching group that contains 2 items, Jebb and Bush (or however many items are in the array).
I've tried this pattern but it only matches the first occurrence: /(?<=category":\[).([^"]*).*?(?=\])/g
Does this match your needs? It should match the category array regardless of its size.
"category":(\[.*?\])
regex101 example
JSON not a regular language. Since it allows arbitrary embedding of balanced delimiters, it must be at least context-free.
For example, consider an array of arrays of arrays:
[ [ [ 1, 2], [2, 3] ] , [ [ 3, 4], [ 4, 5] ] ]
Clearly you couldn't parse that with true regular expressions.
See This Topic:
Regex for parsing single key: values out of JSON in Javascript
Maybe Helpful for you.
Using a set of non-capturing group you can extract a predefined json array
regex answer: (?:\"category\":)(?:\[)(.*)(?:\"\])
That expression extract "category":["Jebb","Bush"], so access the first group
to extract the array, sample java code:
Pattern pattern = Pattern.compile("(?:\"category\":)(?:\\[)(.*)(?:\"\\])");
String body = "{\"device_types\":[\"smartphone\"],\"isps\":[\"a\",\"B\"],\"network_types\":[],\"countries\":[],\"category\":[\"Jebb\",\"Bush\"],\"carriers\":[],\"exclude_carriers\":[]}";
Matcher matcher = pattern.matcher(body);
assertThat(matcher.find(), is(true));
String[] categories = matcher.group(1).replaceAll("\"","").split(",");
assertThat(categories.length, is(2));
assertThat(categories[0], is("Jebb"));
assertThat(categories[1], is("Bush"));
There are many ways. One sloppy way to do it is /([A-Z])\w+/g
Please try it on your console like
var data = '{"device_types":["smartphone"],"isps":["a","B"],"network_types":[],"countries":[],"category":["Jebb","Bush"],"carriers":[],"exclude_carriers":[]}',
res = [];
data.match(/([A-Z])\w+/g); // ["Jebb", "Bush"]
OK the above was pretty sloppy however a solid single regex solution to extract every single element regardless of the number, one by one and to place them in an array (res) is the following...
var rex = /[",]+(\w*)(?=[",\w]*"],"carriers)/g,
str = '{"device_types":["smartphone"],"isps":["a","B"],"network_types":[],"countries":[],"category":["Jebb","Bush","Donald","Trump"],"carriers":[],"exclude_carriers":[]}',
arr = [],
res = [];
while ((arr = rex.exec(str)) !== null) {
res.push(arr[1]); // <- ["Jebb", "Bush", "Donald", "Trump"]
}
Check it out # http://regexr.com/3d4ee
OK lets do it. I have come up with a devilish idea. If JS had look-behinds this could have been done simply by reversing the applied logic in the previous example where i had used a look-forward. Alas, there aren't... So i decided to turn the world the other way around. Check this out.
String.prototype.reverse = function(){
return this.split("").reverse().join("");
};
var rex = /[",]+(\w*)(?=[",\w]*"\[:"yrogetac)/g,
str = '{"device_types":["smartphone"],"isps":["a","B"],"network_types":[],"countries":[],"category":["Jebb","Bush","Donald","Trump"],"carriers":[],"exclude_carriers":[]}',
rev = str.reverse();
arr = [],
res = [];
while ((arr = rex.exec(rev)) !== null) {
res.push(arr[1].reverse()); // <- ["Trump", "Donald", "Bush", "Jebb"]
}
res.reverse(); // <- ["Jebb", "Bush", "Donald", "Trump"]
Just use your console to confirm.
In c++ you can do it like this
bool foundmatch = false;
try {
std::regex re("\"([a-zA-Z]+)\"*.:*.\\[[^\\]\r\n]+\\]");
foundmatch = std::regex_search(subject, re);
} catch (std::regex_error& e) {
// Syntax error in the regular expression
}
If the number of items in the array is limited (and manageable), you could define it with a finite number of optional items. Like this one with a maximum of 5 items:
"category":\["([^"]*)"(?:,"([^"]*)"(?:,"([^"]*)"(?:,"([^"]*)"(?:,"([^"]*)")?)?)?)?
regex101 example here.
Regards.
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.
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);
I'm pushing my values into the array...
while ( ... ) {
push #array, { label => "label", value => "value" };
}
This appears to be working.
Then...
use JSON::PP ;
print JSON::PP->new->utf8->encode(#array) ;
only generates...
{"value":"value","label":"label"}
but I need...
[{"value":"value","label":"label"}{"value":"value","label":"label"} etc.. ]
(each item in array outputted, not just the first one...)
Any ideas?
Try passing a reference to the array:
print JSON::PP->new->utf8->encode(\#array) ;
Encode is documented to take a scalar, not an array (so you need the reference, which is a scalar).