How to iterate through nested arrays

Question

I have data for a table of contents:

array = [
  ['Chapter 1', 'Numbers', 1],
  ['Chapter 2', 'Letters', 72],
  ['Chapter 3', 'Variables', 118]
]

I am trying to display the contents of the array as a table like this:

Chapter 1     Numbers       1
Chapter 2     Letters      72
Chapter 3     Variables   118

Here is my code:

lineWidth = 80
col1Width = lineWidth/4
col2Width = lineWidth/2
col3Width = lineWidth/4

array.each do |i|
  puts i[0].to_s.ljust(col1Width) + puts i[1].to_s.ljust(col2Width) + puts i[2].to_s.ljust(col3Width)
end

The problem is I keep getting this error:

chapter7-arrays.rb:48: syntax error, unexpected tIDENTIFIER, expecting keyword_do or '{' or '('
    puts i[0] + puts i[1] + puts i[2]
                      ^
chapter7-arrays.rb:48: syntax error, unexpected tIDENTIFIER, expecting keyword_do or '{' or '('
    puts i[0] + puts i[1] + puts i[2]

All help appreciated.

Simone Carletti · Accepted Answer · 2015-02-17 21:56:49Z

2

Your code is almost correct. The issue is that you are concatenating multiple puts call, whereas you should concatenate the String arguments, and use a single puts call.

array = [['Chapter 1', 'Numbers', 1],['Chapter 2', 'Letters', 72],['Chapter 3', 'Variables', 118]]

lineWidth = 80
col1Width = lineWidth/4
col2Width = lineWidth/2
col3Width = lineWidth/4

array.each do |i|
    puts i[0].to_s.ljust(col1Width) +
         i[1].to_s.ljust(col2Width) +
         i[2].to_s.ljust(col3Width)
end

answered Feb 17, 2015 at 21:56

Simone Carletti

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4 Comments

sqrcompass Over a year ago

Thanks, Simone! That was embarrassingly "obvious". I am learning to program and this is an interesting phenomena: sometimes the harder I try to solve something, the harder it gets to see the "obvious". It is probably essential to give the brain a rest more frequently...

Daniel Cukier Over a year ago

Since columns 0 and 1 are already strings, there is no need to call to_s on them. The puts would reduce to i[0].ljust(col1Width) + i[1].ljust(col2Width) + i[2].ljust(col3Width)

Simone Carletti Over a year ago

@DanielCukier to_s is required for the third index, otherwise you'll try to call ljust on a Fixnum.

Daniel Cukier Over a year ago

@SimoneCarletti exactly. I forgot to put in code. Here is the right one: i[0].ljust(col1Width) + i[1].ljust(col2Width) + i[2].to_s.ljust(col3Width)

Sergiy Seletskyy · Accepted Answer · 2015-02-19 09:36:37Z

I've added an explanation according to request from dgilperez

We have an array of sub-arrays with three elements in each. And we have three different formatting values for each item in a sub-array. It is convenient to store formatting values in an array too.

lines = [lineWidth/4, lineWidth/2, lineWidth/4]

Now we need to manage a loop for each sub-array

array.each do |i| 
  i.map
end

...and we need an index of the current element to get respective formatting value.

array.each do |i| 
  i.map.with_index
end

Now we implement a block which is executed for each item z of sub-array

i.map.with_index{|z, index| z.to_s.ljust(lines[index])}

... and index is in a range [0,1,2]. So for the first item we will use the first formatting value, etc

index == 0, lines[index] == lineWidth/4

index == 1, lines[index] == lineWidth/2

This block returns an array of strings because we organized a loop via function map. Check map method documentation here

Now we need to concatenate all the strings into one with method join

i.map.with_index{|z, index| z.to_s.ljust(lines[index])}.join

And return the final string - add method puts before the block

puts i.map.with_index{|z, index| z.to_s.ljust(lines[index])}.join

Here is the final code

array = [['Chapter 1', 'Numbers', 1],['Chapter 2', 'Letters', 72],['Chapter 3', 'Variables', 118]]

lineWidth = 80
lines = [lineWidth/4, lineWidth/2, lineWidth/4]

array.each do |i| 
  puts i.map.with_index{|z, index| z.to_s.ljust(lines[index])}.join
end

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