Freemarker: iterate over nested array - arrays

Question

I want to iterate over a nested array I created in Freemarker but can't figure out how to print each value.
The array var
<#assign filters = [
{ "p1" : [ "performance" ] },
{ "p2" : [ "nav" ] },
{ "p3" : [ "quarterly" ] },
{ "f1" : [ "50496", "50497", "50501" ]},
{ "f2" : [ "51202", "51196", "51203", "51246", "51207", "51260" ]},
{ "f3" : [ "50504", "50505", "50506" ]},
{ "f4" : [ "50507", "50508", "50509", "50510", "50512" ]}
]>
Iterating over the array
<#list filters as filter>
${filter}'<#sep>,
</#list>
I want to create an output that looks like this:
$.plugin.function({
p1: 'performance',
p2: 'nav',
p3: 'quarterly',
fi: '50496' + '|' + '50497' + '|' + '50501',
f2: etc....
});
My error is this:
For "${...}" content: Expected a string or something automatically
convertible to string (number, date or boolean),
but this has evaluated to an extended_hash
Any suggestions?

Answer 1

The issue is that Freemarker doesn't have a way to convert filter (a hash) into a string. I think that you want the keys function. Where you now have
${filter}'<#sep>,
You'd instead call
<#list filter?keys as prop>
...
</#list>
and iterate over those keys. In your example there would only be one key per filter and the value
filter[prop]
would be the array, that you'd also have to iterate over.
See Freemarker iterating over hashmap keys

Answer 2

I think you overcomplicate the data structure by using a list of hash-es. Instead, just use a hash:
<#assign filters = {
"p1" : [ "performance" ],
"p2" : [ "nav" ],
"p3" : [ "quarterly" ],
"f1" : [ "50496", "50497", "50501" ],
"f2" : [ "51202", "51196", "51203", "51246", "51207", "51260" ],
"f3" : [ "50504", "50505", "50506" ],
"f4" : [ "50507", "50508", "50509", "50510", "50512" ]
}>
<#list filters?keys as name>
${name}: <#list filters[name] as value>'${value}'<#sep> + '|' + </#list><#sep>,
</#list>
(Another possibility would be a list of lists, but that's less natural.)