Writing a custom sorting lua function

Neovim
1

Hi

I’m trying to get into lua/neovim and have an actual use case that I’d imagine would make a good entry point.

I’d like to write a shopping list, prefix the items with a tag (“d” for dairy etc.) and then have it reformatted (to markdown) and ordered by grocery shop sections.

I’d like to write a function that I can bind to a key that does some formatting and sorting to a selection:
Input

m chicken
p tomatoes
p cucumbers
d milk
d mozzerella
m ham

desired output (in place replacement of visual selection)

## meat
- [ ] chicken
- [ ] ham

## produce
- [ ] tomatoes
- [ ] cucumbers

## dairy
- [ ] milk
- [ ] mozzerella

Now I do have programming knowledge alongside some basic lua knowledge and writing the sorting and formatting part would be no big deal. But I have no idea about vim/lua scripting for (neo)vim.

I took a look at Getting started using Lua in Neovim but this seems to be more about using lua in neovim.

I have some general questions:

  • I’m assuming this can be achieved via a function written in your init.lua config file or outside it and then import/require it (so no need to write a plugin), right?
  • How would I be able to pass the visual selection to the function or retrieve it inside the function? I searched some docs and found stuff like nvim_win_get_cursor({window}) but couldn’t find information about how to get visual selection.
  • How would I go about replacing the visual selection with the reformatted code?

Any pointers on how to do this or where to find resources about it are greatly appreciated.

Cheers!

2

Yes, that is correct.

Here’s a quick-and-dirty implementation I came up with that mostly does what you ask which you can hopefully use as a reference/starting point:

function convert_to_list(category_map, category_len)
  category_len = category_len or 1

  -- Adapted from https://stackoverflow.com/a/6271254, for how to get visual styled
  -- selection. Not sure this is the best way but it seems to work.
  local _, lnum_start = unpack(vim.fn.getpos("'<"))
  local _, lnum_end = unpack(vim.fn.getpos("'>"))
  local lines = vim.api.nvim_buf_get_lines(0, lnum_start - 1, lnum_end, true)
  local categories = {}
  for _, line in ipairs(lines) do
    local category = line:sub(1, category_len)
    if category_map then
      category = category_map[category]
    end

    -- +2 since we assume there's a space in between the category names
    -- and the items
    local item = line:sub(2 + category_len, -1)
    if not categories[category] then
      categories[category] = {
        item
      }
    else
      table.insert(categories[category], item)
    end
  end

  local new_lines = {}
  for category, items in pairs(categories) do
    -- Here `##` is assumed to be used for headers and `- [ ]` for items, but
    -- you could pretty easily make that configurable via an `options` table param.
    table.insert(new_lines, '## ' .. category)
    for _, item in ipairs(items) do
      table.insert(new_lines, '- [ ] ' .. item)
    end

    table.insert(new_lines, '')
  end

  vim.api.nvim_buf_set_lines(0, lnum_start - 1, #new_lines, false, new_lines)
end

Note that there at the bottom you can see how the text is inserted, via nvim_buf_set_lines; see :help nvim_buf_set_lines() and you may also want to check out :help nvim_buf_get_lines().

You can try this out by first running :luafile % with a Lua file open and focused containing the above code, then switch to another file with your input in it, select it with visual mode, and then run :lua convert_to_list({ p = 'produce', d = 'dairy', m = 'meat' }, 1). Should result in basically the output that you wanted.

Of course, this likely doesn’t handle certain edge cases, do exactly what you want, etc., but hopefully it gives you a decent starting point. Happy to answer any questions about the above as I’m able (like how to turn this into a requireable module, for example, since defining a global function probably isn’t ideal).

EDIT: Found vim - How to get visually selected text in VimScript - Stack Overflow so updated answer to use visual selection.

3

Wow, cool. Thank you very much. I’ll check it out once I got a minute!