Checking variables exist before building an array

Question

I am generating a string from a number of components (title, authors, journal, year, journal volume, journal pages). The idea is that the string will be a citation as so:

@citation = article_title + " " + authors + ". " + journal + " " + year + ";" + journal_volume + ":" + journal_pages

I am guessing that some components occasionally do not exist. I am getting this error:

no implicit conversion of nil into String

Is this indicating that it is trying to build the string and one of the components is nil? If so, is there a neat way to build a string from an array while checking that each element exists to circumvent this issue?

if doesn't exist what you want to output ?

Arup Rakshit
– Arup Rakshit

2015-03-22 16:43:27 +00:00
Commented Mar 22, 2015 at 16:43 — Arup Rakshit
– Arup Rakshit, Commented Mar 22, 2015 at 16:43

Mohammad AbuShady · Accepted Answer · 2015-03-22 16:44:14Z

4

It's easier to use interpolation

@citation = "#{article_title} #{authors}. #{journal} #{year}; #{journal_volume}:#{journal_pages}"

Nils will be substituted as empty strings

answered Mar 22, 2015 at 16:44

Mohammad AbuShady

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GhostRider Over a year ago

This works beautifully. Many thanks. Will accept when the timer allows me too....cheers Pal.

Arup Rakshit · Accepted Answer · 2015-03-22 16:47:16Z

array = [ article_title, authors ,journal, year, journal_volume, journal_pages ] @citation = "%s %s. %s %s; %s:%s" % array

Use String#% format string method.

Demo

>> "%s: %s" % [ 'fo', nil ] => "fo: "

This also works but for reasons I haven't explained above, the solution of Mohammad AbuShady fits better with my needs. Many thanks Arup.

Cary Swoveland · Accepted Answer · 2015-03-23 00:15:43Z

Considering that you presumably are doing this for more than one article, you might consider doing it like so:

SEPARATORS = [" ", ". ", " ", ";", ":", ""] article = ["Ruby for Fun and Profit", "Matz", "Cool Tools for Coders", 2004, 417, nil] article.map(&:to_s).zip(SEPARATORS).map(&:join).join # => "Ruby for Fun and Profit Matz. Cool Tools for Coders 2004;417:"

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