Build an array using inject

Question

I'm trying to build an array using inject. I expect consents to be an array of ParticipantConsent objects.

Each ParticipantConsent object can :have_many ParticipantConsentSample objects.

I expect sc to contain an array of arrays of ParticipantConsentSample objects associated with every ParticipantConsent object associated with a Participant.

consents = ParticipantConsent.where(:participant_id => @participant.id).all
sample_consents = consents.inject { |sc, c| sc << ParticipantConsentSample.where(:participant_consent_id => c.id).all }

Currently getting back the contents of consents when I check the contents of sample_consents. Where am I going wrong? Thanks.

dbenhur · Accepted Answer · 2013-05-17 17:37:57Z

3

Since you just want an array of arrays obtained from ParticipantConsentSample, you don't really want inject, you want map:

sample_consents = consents.map do |c|
  ParticipantConsentSample.where(:participant_consent_id => c.id).all
end

answered May 17, 2013 at 17:37

dbenhur

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Comments

Arup Rakshit · Accepted Answer · 2014-12-13 12:46:16Z

3

try the below:

sample_consents = consents.inject([]) do |sc, c| 
  sc << ParticipantConsentSample.where(participant_consent_id: c.id).to_a
  sc
end

edited Dec 13, 2014 at 12:46

user2611793

answered May 17, 2013 at 17:06

Arup Rakshit

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2 Comments

user2611793 Over a year ago

I cleaned up your code but you don't need an inject for a simple array. Just use a map.

MatzFan Over a year ago

No need for standalone sc line in the block, as it is returned from the previous line. Don't you love Ruby :)

Zach Kemp · Accepted Answer · 2013-05-17 17:06:05Z

2

If you want sample_consents to be an array, you need to initialize it as one using an argument to inject:

sample_consents = consents.inject([]) { |sc, c| ... }

answered May 17, 2013 at 17:06

Zach Kemp

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1 Comment

user2611793 Over a year ago

This is a terrible example because it ignores the trap that new Ruby programmers can get caught in: the injected value must be the last line of the injection block.

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