table.sort() question

Getting Started Newbie Questions
#1

Here is the link for the API reference: https://docs.coronalabs.com/api/library/table/sort.html

I was looking at this function and had some questions about how to get it to work for my situation.

I have a table as follows

local spots = { [1] {X = 100, Y = 100, Distance = 350}, [2] {X = 75, Y = 150, Distance = 450}, [3] {X = 150, Y = 200, Distance = 100}, [4] {X = 100, Y = 120, Distance = 200}, }

The table.sort() function API doesn’t seem to go into painful detail about how to set up the function.

I would like for it to look at my table and compare the Distance values and sort them in ascending order, so the smallest distance is in spots[1].

I was hoping maybe someone could explain a little bit about the API page and explain to me what the “a, b” would reference in the example and how I could set up the function to get it to sort depending on the distance value.

Thanks guys 

#2

The idea for the sort function is you will get two values passed to it, the items to compare. Sort looks at two table rows at a time to decide which is the larger value. In your case, you’re passing in tables for each row. Something like:

local function compare( a, b ) &nbsp;&nbsp;&nbsp; return a.Distance \< b.Distance end

or something like that.

Rob

#3

It is on the docs:

This compare function receives two arguments and must return true if the first argument should come first in the sorted array

So, for you case it would be:

local function compare( a, b ) return a.Distance \< b.Distance end table.sort( spots, compare )
#4

Thanks guys, I appreciate the help

#5

ok, so I tested the solutions you guys provided by putting this into my code after the table

local function compare( a, b ) return a.Distance \< b.distance end spots.sort( spots, compare )

but then I get an error that states “Attempt to call field ‘sort’ (a nil value)”

I can’t image what would be causing this issue…

#6

im an idiot… I should have put table.sort( spots, compare)… Sorry guys

#7

I’d check my case too:

return a.Distance \< b.distance

versus

return a.Distance \< b.Distance
#8

The idea for the sort function is you will get two values passed to it, the items to compare. Sort looks at two table rows at a time to decide which is the larger value. In your case, you’re passing in tables for each row. Something like:

local function compare( a, b ) &nbsp;&nbsp;&nbsp; return a.Distance \< b.Distance end

or something like that.

Rob

#9

It is on the docs:

This compare function receives two arguments and must return true if the first argument should come first in the sorted array

So, for you case it would be:

local function compare( a, b ) return a.Distance \< b.Distance end table.sort( spots, compare )
#10

Thanks guys, I appreciate the help

#11

ok, so I tested the solutions you guys provided by putting this into my code after the table

local function compare( a, b ) return a.Distance \< b.distance end spots.sort( spots, compare )

but then I get an error that states “Attempt to call field ‘sort’ (a nil value)”

I can’t image what would be causing this issue…

#12

im an idiot… I should have put table.sort( spots, compare)… Sorry guys

#13

I’d check my case too:

return a.Distance \< b.distance

versus

return a.Distance \< b.Distance