# How to flatten and remove duplicates in query results?
**URL:** https://community.silverbullet.md/t/how-to-flatten-and-remove-duplicates-in-query-results/3397
**Category:** Lua
**Created:** [October 15, 2025, 7:44pm UTC](https://community.silverbullet.md/t/how-to-flatten-and-remove-duplicates-in-query-results/3397 "2025-10-15T19:44:51Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@thick.cliff](https://community.silverbullet.md/u/thick.cliff)
#### Post date: [October 15, 2025, 7:44pm UTC](https://community.silverbullet.md/t/how-to-flatten-and-remove-duplicates-in-query-results/3397/1 "2025-10-15T19:44:51Z")
Using the following query I get a list of arrays. I want to flatten these arrays into one array and remove duplicates. Not sure what built in functions are available.
```auto
${query[[
from index.tag "page"
where name:startsWith("Journal/")
select {
Tags = _.tags
}
]]}
```
Here is my best failed attempt
```auto
${query[[
from index.tag "page"
where name:startsWith("Journal/")
select {
Tags = utils.unique(utils.flatten(_.tags))
}
]]}
-- Flattens a list of lists into a single list
function utils.flatten(list_of_lists)
local flat = {}
for _, sublist in ipairs(list_of_lists) do
for _, value in ipairs(sublist) do
table.insert(flat, value)
end
end
return flat
end
-- Removes duplicates from a list while preserving order
function utils.unique(list)
local seen = {}
local result = {}
for _, value in ipairs(list) do
if not seen[value] then
seen[value] = true
table.insert(result, value)
end
end
return result
end
```
---
### Author:  [@markalex](https://community.silverbullet.md/u/markalex)
#### Post date: [October 16, 2025, 3:18pm UTC](https://community.silverbullet.md/t/how-to-flatten-and-remove-duplicates-in-query-results/3397/2 "2025-10-16T15:18:43Z")
In general, I would like to know how to flatten arrays in lua too.
But for a specific usecase similar to yours, I’m using a workaround:
```auto
${query[[
from index.tag "tag"
where _.parent == "page" and page:startsWith("Journal/")
]]}
```
---
### Author:  [@thick.cliff](https://community.silverbullet.md/u/thick.cliff)
#### Post date: [October 16, 2025, 7:03pm UTC](https://community.silverbullet.md/t/how-to-flatten-and-remove-duplicates-in-query-results/3397/3 "2025-10-16T19:03:04Z")
> [@markalex](#):
>
> ```auto
> ${query[[
> from index.tag "tag"
> where _.parent == "page" and page:startsWith("Journal/")
> ]]}
>
> ```
Thanks, that worked! This is what I ended up with.
```auto
${query[[
from index.tag "tag"
where _.parent == "page" and page:startsWith("Journal/")
select "[[" .. _.name .. "]]"
]]}
```
Does silverbullet have any documentation about the object model?
---
### Author:  [@markalex](https://community.silverbullet.md/u/markalex)
#### Post date: [October 16, 2025, 7:25pm UTC](https://community.silverbullet.md/t/how-to-flatten-and-remove-duplicates-in-query-results/3397/4 "2025-10-16T19:25:36Z")
This obviously depends on how you use tags in your instance, but format `"[[" .. _.name .. "]]"` for tags looks a bit odd to me.
In my instance I have a list of tags that are attached to tasks shown like this:
```auto
${template.each(query[[
select {name=_.name}
from index.tag "tag"
where _.parent == "task"
]], template.new[==[#${name}]==])}
```
It ensures that tags are rendered as a tag (with all your custom styling still in place), and link to virtual page also is there.
---
### Author:  [@thick.cliff](https://community.silverbullet.md/u/thick.cliff)
#### Post date: [October 16, 2025, 10:12pm UTC](https://community.silverbullet.md/t/how-to-flatten-and-remove-duplicates-in-query-results/3397/5 "2025-10-16T22:12:10Z")
> [@markalex](#):
>
> ```auto
> ${template.each(query[[
> select {name=_.name}
> from index.tag "tag"
> where _.parent == "task"
> ]], template.new[==[#${name}]==])}
>
> ```
That’t better than what I did, thanks