Michael Malura # Ramda - Validate sequence of numbers

I need to verify that i don't miss any events. So i came up with the concept of a number which needs to increment with every event.

If the numbers aren't consecutive i can tell that the collection is not valid.

## Dataset

``````const data = {
'transactions': [{
'transaction': 'A',
'events': [{
'number': 0 // <-- Valid
}, {
'number': 1 // <-- Valid
}]
}, {
'transaction': 'C',
'events': [{
'number': 5 // <-- Valid
}, {
'number': 6 // <-- Valid
}]
}, {
'transaction': 'B',
'events': [{
'number': 3,
}, {
'number': 10,  // <-- Not valid because there are some events are missing
}]
}]
};
``````

## Code

``````const eventsAreIncrementing = R.pipe(
R.sortBy(R.prop('number')), // Sort events
R.map(R.prop('number')), // Get list of event numbers
R.reduce((acc, current) => {
if (acc === false) return false; // Skip if we already found a faulty value
// For the first element return the current one
// or
// Check if the current element is an increment of the one before
if (acc === null || acc + 1 === current) { return current; }
return false; // Return false to signal that the sequence is not incrementing by one
}, null),
R.is(Number) // Reduce returns false if the numbers aren't consecutive otherwise it returns the last number.
// This is why i check if the result is a number.
);
const allEventsAreIncrementing = R.pipe(
R.map(R.prop('events')),
R.all(eventsAreIncrementing)
);
const valid = allEventsAreIncrementing(data.transactions);
``````