Load a table

A small bakery keeps a week of its sales, Monday to Sunday, in a CSV file. In this step your app reads that file, counts its rows and shows them in a table.

Load the file

Make a folder for this tutorial. Inside it, save these rows as data/sales.csv:

day,item,sold
1,Bread,42
1,Buns,18
1,Cake,6
2,Bread,38
2,Buns,22
2,Cake,5
3,Bread,45
3,Buns,20
3,Cake,9
4,Bread,40
4,Buns,25
4,Cake,7
5,Bread,52
5,Buns,31
5,Cake,12
6,Bread,61
6,Buns,40
6,Cake,21
7,Bread,55
7,Buns,36
7,Cake,25

Then save this program as view.lua, next to the data folder:

local data = datumhue.args.dirs.data
local sales = data:read("sales.csv"):csv()

print("rows: " .. sales:count())

In this example: datumhue.args Dir:read Bytes:csv DataHandle:count

Your app cannot open a path by itself. It reads files through handles it is given when it starts. Run it with the data folder granted to it under the name data:

$ datumhue run view.lua --dir data:data

It prints rows: 21 and keeps its empty window open until you close it.

• --dir data:data grants the folder data, read-only, under the name before the colon. Your app finds it in datumhue.args and never sees the folder's path.
• Dir:read returns the file as a Bytes handle at once. The file is read when you decode it.
• Bytes:csv decodes the bytes into a DataHandle, a table kept outside Lua. The first row of the file names its columns.
• DataHandle:count waits for the file to load, then counts its rows.

Show it in a table

Replace the print with a page that shows the rows:

New line: local ui = datumhue.ui
local data = datumhue.args.dirs.data
local sales = data:read("sales.csv"):csv()

New line: local page = ui.root:panel({
New line:     width = "100%",
New line:     height = "100%",
New line:     flex_direction = "column",
New line:     padding = 16,
New line:     gap = 12,
New line: })
New line: page:label({
New line:     text = "Bakery sales: " .. sales:count() .. " rows",
New line:     font_size = 20,
New line: })
New line: page:table({
New line:     data = sales,
New line:     columns = {
New line:         { column = "day", label = "Day" },
New line:         { column = "item", label = "Item" },
New line:         { column = "sold", label = "Sold" },
New line:     },
New line:     flex_grow = 1,
New line: })

In this example: datumhue.ui datumhue.args Dir:read Bytes:csv datumhue.ui.root UiElement:panel UiElement:label DataHandle:count UiElement:table

Run it with the same command. A heading gives the row count, and the week's sales fill a table below it.

• The page is a panel that fills the window and stacks what it holds in a column, 12 UI px apart.
• UiElement:table shows a DataHandle, with one column for each entry in columns. It reads only the rows in view and never copies the table into Lua.
• flex_grow = 1 gives the table the room the heading leaves. It scrolls when its rows do not fit.