Linq: Select all items in 1 list where they almost match an item in another list [closed]

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I have a list of Objects which have a location [Rect].

I then select from this list, all Rects that fall inside a 'Column' (Left>x1 && Right<x2)

What I need to to now is find all Rects that are (roughly) in-line horizontally with each item in that list.

The only way I have found so far is to iterate over the list and check each rect individually for its Top value, but I feel this should be a lambda function.

Iterating code is as follows:

// Find all shapes on the page within these bounds
var BottomLeft = new Point(50, 45);
var TopRight = new Point(430, 770);

var allRects = allShapes.Where(sh => sh.BoundingBox.Bottom >= BottomLeft.Y
&& sh.BoundingBox.Left >= BottomLeft.X
&& sh.BoundingBox.Top <= TopRight.Y
&& sh.BoundingBox.Right <= TopRight.X).OrderByDescending(tb => tb.BoundingBox.Top);

// Select the rightmost column
var Col = allRects.Where(rt => rt.BoundingBox.Left > 365);

foreach (var rt in Col)
{
    var rct = allRects.Where(tb => Math.Abs(tb.BoundingBox.Top - rt.BoundingBox.Top) < 2);
    /// etc...
    
}

How would I convert the foreach loop into a lambda query?

FYI: you have multiple enumerations of sequence with OrderByDescending - that's an expensive operation — ASh
– ASh, Commented Jun 20 at 11:12
So would it be better to order the list at the very end of the process? Just trying to save as much processing time as I can. — Richard Harrison
– Richard Harrison, Commented Jun 20 at 11:36
Please finish the etc... part, or tell us what the result should be, why did you think this should be a lambda function? — shingo
– shingo, Commented Jun 20 at 12:18
I agree with @shingo - the etc... is the most important part to understand what your expected result is. — Jeanot Zubler
– Jeanot Zubler, Commented Jun 20 at 13:00

Nico Volling · Accepted Answer · 2025-06-20 14:40:11Z

1

You can convert your foreach loop into a LINQ expression using Select to project each rt from Col along with its horizontally-aligned matches from allRects. Here's how it could look:

var alignedGroups = Col
    .Select(rt => new
    {
        Reference = rt,
        Aligned = allRects.Where(tb => Math.Abs(tb.BoundingBox.Top - rt.BoundingBox.Top) < 2)
    });

This gives you an IEnumerable of anonymous objects, each containing a Reference rect (rt) and a list of Aligned rects that are roughly on the same horizontal line (within ±2 units in Y).

If you want just a flat list of all aligned rects (without grouping them by reference), you could use SelectMany:

var alignedRects = Col
    .SelectMany(rt => allRects.Where(tb => Math.Abs(tb.BoundingBox.Top - rt.BoundingBox.Top) < 2));

This mirrors the logic from your loop, just in a more functional (lambda) style.

answered Jun 20 at 14:40

Nico Volling

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1 Comment

Richard Harrison Jun 24 at 6:51

Perfect.... That was exactly what I was looking for. Thank you.

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