32 — Grade book: a score per name, and an average

A grade book is one score under each name. But working out an average needs the scores on their own — a record has no order and no total. So the record is walked and the scores are copied into a list.

#Steps

1. Put the names and scores in a record:

   set marks to an empty record
   put Mina at 88 in marks
   put Sana at 92 in marks
   show Mina in marks
   

   copyrun it →

   You get 88.

2. Walk it and collect the scores into a list. Only a list can be asked for a total and a count:

   set marks to an empty record
   put Mina at 88 in marks
   put Sana at 92 in marks
   set scores to an empty list
   for each name in marks
       set score to name in marks
       append score to scores
   end
   show how many scores
   show the total of scores
   

   copyrun it →

   2 and 180.

3. The average is the total divided by the number of people. Put the divisor in a name first:

   set scores to list of 88, 92
   set people to how many scores
   set average to the total of scores
   divide average by people
   show average
   

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   You get 90.0. What you divide by has to be a name or a number — divide average by how many scores is not a thing, which is why people holds it first.

4. The best score the list answers directly:

   set scores to list of 88, 92, 75
   show the biggest of scores
   

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   You get 92.

5. The whole thing:

   set marks to an empty record
   put Mina at 88 in marks
   put Sana at 92 in marks
   put Ada at 75 in marks
   set scores to an empty list
   for each name in marks
       set score to name in marks
       append score to scores
       show name
       show score
   end
   set people to how many scores
   set average to the total of scores
   divide average by people
   show average
   show the biggest of scores
   

   copyrun it →

#Try it yourself

Pick out everyone above the average — walk the record a second time and show the name when if score is greater than average. It has to be a second walk: during the first one the average does not exist yet.

#What you learned

• A record is for looking up by name; a list is for totals, counts and the biggest.
• Walking a record and copying its values into a list gets you both.
• The average is the total divided by the count, and the divisor must be a name or a number.
• A comparison against an average happens after the average is finished.