Flowcharts with filters: make every path finish a visit

A filtered flowchart adds another decision inside the loop. One decision asks whether work remains. The next asks whether the current card should update the answer.

Separate the loop test from the filter test #

“More cards?” decides whether to start another visit. “X.group = F?” decides what to do with the card already picked. A No at the filter does not mean the dataset is finished: continue to the next card.

One-group sum #

Start Sum at 0. On a matching F card, add its maths mark. On a non-matching card, do not change Sum. In both cases move the card to Pile 2 and return to the availability test. For the six teaching marks cards, the F total is 68+57+87 = 212.

Two-group sums in a single scan #

Initialize FSum and MSum to zero. For a valid dataset whose group labels are exactly F and M, the filter’s Yes branch can update FSum and its No branch can update MSum. Both branches join before the loop continues. If other labels or missing values are allowed, do not automatically treat every non-F value as M; validate the labels or add an explicit branch.

Tutorial flowchart: all food and no food #

AllFoodCount ← 0
NoFoodCount ← 0
For each nonempty shopping bill X:
    If every item in X is Food:
        AllFoodCount ← AllFoodCount + 1
    Else if no item in X is Food:
        NoFoodCount ← NoFoodCount + 1
    Move X to the visited pile

For the teaching bills [rice,milk], [soap,notebook], [rice,soap], [milk], the final counts are AllFoodCount = 2 and NoFoodCount = 1. The mixed bill updates neither. Draw the mixed path too: it must rejoin the loop just like the two updating paths.

Audit a flowchart with four questions #

Is every variable initialized before use? Does every True/False branch have a destination? Does every completed visit mark or move the card? Does every continuing path return to the correct test? A missing path can skip records, stop early or repeat a card forever.

Source: Lecture 1.5; Tutorial 1.3 — Tutorial for Lecture 5. Small teaching datasets and diagrams are prepared for these notes; lecture and tutorial totals are identified explicitly.