Convert nested CSV data file to JSON - json

Question

I am trying to create a Perl function which converts CSV with a special format to JSON.
I have a CSV file where every line has the following format
child_number,parent_number,status
The root parent (without a parent) has parent_number = NA.
My goal is to convert into JSON format like this
{
number:
status:
children: [
{
number:
status:
children: [
{
number:
status:
}
]
},
number:
status:
children: [
{
number:
status:
}
]
]
}
I inserted the contents of the CSV file into an array and found the line with no parent
foreach my $line ( #csv_arr ) {
($child, $perent, $status) = split(/,/,$line);
last if ( $perent eq "NA" );
}
return 0 unless($perent eq "NA");
I would like to get the children for each $perent and insert them into the data structure. I could use the following
push #{ $json_struct->{usage} }, {
number => $perent,
children => getChildren(),
};
...
my #json_arr = JSON::PP->new->encode($json_struct);
In order to explain myself better, please consider the following example
> cat ./csv_file
7,5,0
5,NA,0
3,5,1
> cat ./json_file
{
number: NA
status: 0
children: [
{
number: 5
status: 0
children: [
{
number: 3
status: 1
},
{
number: 7
status: 0
}
]
}
]
}
These are the contents of the CSV file after a real run
7696,44641,0
44654,44641,0
44646,44641,0
44644,44641,0
44651,44649,0
7700,44641,0
7691,44641,0
44657,44641,0
7699,7698,0
7692,44641,0
44650,44649,0
44661,44660,0
44656,44654,1
44659,44641,0
44648,44646,0
7695,7694,0
44662,44660,0
44641,NA,0
7701,7700,0
7698,44641,0
44653,44651,1
44645,44644,0
44647,44646,0
44649,44641,0
44660,44641,0
7697,7696,0
7689,7688,0
7694,44641,0
44658,44657,1
7693,44641,0
7688,44641,0
What is the proper way to implement this method in Perl?

Answer 1

Here's one way to do it:
use strict;
use warnings;
use JSON::PP ();
my %nodes;
$nodes{NA} = { number => 'NA', status => 0 };
while (my $line = readline DATA) {
chomp $line;
my ($id, $parent_id, $status) = split /,/, $line;
my $node = $nodes{$id} //= {};
$node->{number} = 0 + $id;
$node->{status} = 0 + $status;
push #{ $nodes{$parent_id}{children} }, $node;
}
my $jsonpp = JSON::PP->new->pretty->canonical;
print $jsonpp->encode($nodes{NA});
__DATA__
7,5,0
5,NA,0
3,5,1
Output:
{
"children" : [
{
"children" : [
{
"number" : 7,
"status" : 0
},
{
"number" : 3,
"status" : 1
}
],
"number" : 5,
"status" : 0
}
],
"number" : "NA",
"status" : 0
}
The only reason
$nodes{NA} = { number => 'NA', status => 0 };
is there is to give the root node a number and status field. It doesn't otherwise exist in your CSV input, so without that line you'd get a root object containing only a children field.
For every CSV record we extract its id, the corresponding parent id, and the status.
If we've already created a node for this id (this happens if another node has already specified this node as its parent), we just use the existing node; otherwise we create a new empty node and store it in %nodes.
%nodes is our universe of nodes indexed by their id.
We always set the number and status fields. The 0 + part is to explicitly convert the values to numbers (otherwise they'd be quoted in the JSON output).
We add our current node to the list of children of its parent (which is found in $nodes{$parent_id}{children}).
At the end we simply pretty-print the tree under $nodes{NA}, including its children, their children-children, and so on.