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I am trying to go through each of the books in holds using holds[0], holds[1] etc and test to see if the title is equal to a book title

Translated almost literally to Python:

Mind that if people update their Google Form response, the submission row in the spreadsheet will not change - only the content.

• You can retrieve the latest submitted / modified form response row with the event object event.range (provided your function is bound to a Google Sheets form submit trigger)
• You can compare the modified row to the last row in the sheet
• If the form response row is equal to the last row - a new response has been submitted

Sample:

You should call the function like this checkBasket(amazonBasket, "camera"); instead where amazonBasket is an object and camera is the key you want to look up.

A better/cleaner solution would be

imageLinks in volumeInfo isn't available for every book

for example

https://www.googleapis.com/books/v1/volumes?q=test

the '0' book "Software-Test für Embedded Systems" doesn't contain imageLinks

you need to try/catch that case or look beforehand if it exists

I am not sure when and how I do the Vars^Goal (existentially quantifying) in Prolog.

The easiest answer is: Don't do it, ever. You can always introduce an auxiliary predicate that captures exactly the query you want, exposing exactly the arguments you want and nothing else (that would require quantification), and with a nice self-documenting name.

In your example, you can define:

This seems to do the trick:

Let's say we have 2 components

1. BooksHome for /books/
2. SingleBook for /books/:id

So when the user visits /books/ route, fire a thunk fetchBooks(..) which loads books and saves them in state.bookstore.books and display those books in BooksHome

And when the user visits /books/:id route, fire a thunk fetchSingleBook(..) which will find book item with :id in state.bookstore.books if that's present return it and display it in SingleBook and if it's not there, fetch it, add it to state.bookstore.books and return it and display it in SingleBook.

Explanation:

When the user visits /books/123 right away, state.bookstore.books is [] so no item is found, so we'll fetch it, store it and display it.

When the user visits /books/ (data fetched and stored) and then visits /books/123, state.bookstore.books is having an item with id:123 so the item is found, so we'll get it from state.bookstore.books and display it.

Must do things:

1. fetchBooks must be dispatched in BooksHome but not in App
2. Same way fetchSingleBook must be dispatched in SingleBook

Things optimised with this approach:

1. We need not fetch all books for displaying a single book.
2. We need not re-fetch book's data when it is already available in state.bookstore.books

Hope this helps🤝

I have added two new sheets: "Erik Help" and "Authors".

The "Authors" sheet contains a single IMPORTRANGE formula in A1, which brings in all the data from your source spreadsheet. Then, formulas within the current spreadsheet can simply refer to the data in the "Author" page, instead of using more IMPORTRANGE references.

From there, I reference the "Author" sheet within one formula in C1 of "Erik Help" (i.e., the "ID" column):

=ArrayFormula({"ID";IF(A2:A="";;SUBSTITUTE(TRIM(TRANSPOSE(QUERY(TRANSPOSE(ARRAY_CONSTRAIN(IFERROR(VLOOKUP(TRIM(SPLIT(B2:B&REPT(",X";10);","));{Authors!B:B\Authors!A:A};2;FALSE));ROWS(A2:A);10));" ";10)));" ";", "))})

This one formula creates the header and all results for the column.

The formula itself is difficult to explain. But below are some of the key concepts.

REPT adds 10 repetitions of ",X" to the end of every string in B2:B. This assures that, when SPLIT we will have at least 10 items for each row. I chose the number 10, because it seems likely that no book will have more than 10 authors; and we will need uniformity for the rest of the formula.

SPLIT splits the string of author names and X'es into separate columns at the commas.

TRIM will remove extra spaces.

VLOOKUP will attempt to find every separate author name or X in a reversed array from the "Author" sheet, returning the ID number if found.

IFERROR will return null if nothing is found (which of course will happen for each X).

ARRAY_CONSTRAIN will limit the returned results to 10 virtual columns.

TRANSPOSE(QUERY(TRANSPOSE(... will create QUERY headers from all 10 results per row and then flip them to match the row-by-row data.

TRIM again makes sure there are no stray spaces.

SUBSTITUTE will exchange remaining spaces for ", ".