Algorithm and iteration with Power BI / DAX

Hi Ben75 

For your question, here is the method I provided:

Note whether the correct relationship exists between the two tables.

First, you need to create two MEASURES to calculate the cumulative sum of each fruit in the order and to sort the order.

Rank = 
RANKX(
    FILTER(
        ALL('Orders'), 
        'Orders'[Fruit] = MAX('Orders'[Fruit])
    ), 
    CALCULATE(SELECTEDVALUE(Orders[Order ID])),,ASC, Dense
)

total orders = 
CALCULATE(
    SUM('Orders'[Quantity requested]), 
    FILTER(
        ALL('Orders'),
        'Orders'[Fruit] = MAX('Orders'[Fruit])
        &&
        'Orders'[Order ID] <= MAX('Orders'[Order ID])
    )
)

Create measures.

Quantity available = 
var _fruit = SELECTEDVALUE('Fruits'[Quantity available])
var _orderTotal = 
    CALCULATE(
        SUM('Orders'[Quantity requested]), 
        FILTER(
            ALL('Orders'), 
            'Orders'[Fruit] = MAX('Orders'[Fruit])
        )
    )
var _QuantityAvailable = _fruit - _orderTotal
RETURN
IF(_QuantityAvailable > 0, _QuantityAvailable, 0)

Quantity delivered = 
var _minRank = MINX(FILTER(ALL('Orders'), 'Orders'[Fruit] = MAX('Orders'[Fruit])), 'Orders'[Rank])
RETURN
IF(
    SELECTEDVALUE('Fruits'[Fruit]) = SELECTEDVALUE('Orders'[Fruit]), 
    IF(
        SELECTEDVALUE('Fruits'[Quantity available]) - 'Orders'[total orders] > 0,
        SELECTEDVALUE('Orders'[Quantity requested]), 
        IF('Orders'[Rank] = _minRank + 1,
        SELECTEDVALUE('Fruits'[Quantity available]) -
        CALCULATE(
            SELECTEDVALUE('Orders'[Quantity requested]),
            FILTER(
                ALL('Orders'),  
                'Orders'[Fruit] = MAX('Orders'[Fruit]) 
                &&
               'Orders'[Rank] = _minRank)
            ),
            0
        )
    ),        
    BLANK()
)

As for the COMMENT section being displayed according to your table, I'm afraid that's difficult to achieve.

Here is the result.

I hope this helps you.

Regards,

Nono Chen

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