Parse JSON output into a CSV file using Powershell - powershell

Question

I'm using PowerShell to extract data via an API and would like to parse the JSON into a CSV file. How would I parse each of the JSON results into a CSV structure like this:
$Date, $app, $pagename, $range1, $range1_value
$Date, $app, $pagename, $range2, $range2_value
$Date, $app, $pagename, $range3, $range3_value
The JSON looks like this:
{
"fields": [
{
"label": "app",
"field": "app",
"type": "string"
},
{
"label": "pagename",
"field": "pagename",
"type": "string"
},
{
"label": "range1",
"field": "count(*)",
"type": "integer",
"aggregation": "filter"
},
{
"label": "range2",
"field": "count(*)",
"type": "integer",
"aggregation": "filter"
},
{
"label": "range3",
"field": "count(*)",
"type": "integer",
"aggregation": "filter"
}
],
"results": [
[
"application1",
"loginpage",
41425,
41266,
18869
],
[
"application2",
"loginpage",
7424,
7113,
2905
]
],
"moreData": false,
"schema": "record"
}
I've tried various methods (e.g. Convertto-JSON and Convertfrom-JSON) but I don't seem to be able to connect the 'fields' and 'results' together into a hashtable. I was hoping I could create it as a $JSON object and then iterate through each result like $JSON[0..1].

Answer 1

Let's start by parsing your input data!
Use a for loop to iterate over the individual array items in the results values, then use the index to resolve the type and label name from the fields list:
# Convert from json
$data = $jsonString |ConvertFrom-Json
# Set up a type table for easy conversion
$typeTable = #{'integer' = [int]}
# Iterate over each row in the results
$results = foreach($values in $data.results){
# Create dictionary to hold property values for the row
$Properties = [ordered]#{}
for($index = 0; $index -lt $data.fields.Count; $index++){
# Resolve field metadata by index
$field = $data.fields[$index]
# Take type mappings into account and write to $Properties dictionary
if($typeTable.ContainsKey($field.type)){
$Properties[$field.label] = $values[$index] -as $typeTable[$field.type]
}
else{
$Properties[$field.label] = $values[$index]
}
}
# Output structured object
[PSCustomObject]$Properties
}
Now that we have nice objects we can work with, we can use Select-Object and Export-Csv to create the desired output format:
$results |Select-Object #{Name='Date';Expression={Get-Date -Format yyyyMMdd}},app,pagename,#{Name='2000';Expression={'2000'}},range3 |Export-Csv -Path .\path\to\output.csv -NoTypeInformation