How to Concatenate Integer Array to Single Integer in Ruby

Just join the array and convert the resulted string to an integer:

[1,2,3].join.to_i

ruby arrays concatenation

If you want to avoid converting to and from a String, you can use inject:

[1,2,3].inject{|a,i| a*10 + i}#=> 123

ruby arrays concatenation

Personally I would use

Integer([1,2,3].join, 10) #=> 123

since it has the nice side-effect of throwing an exception that you can deal with if you have non-numeric array elements:

>> Integer([1,2,'a'].join, 10) # ArgumentError: invalid value for Integer: "12a"

Compare this to to_i:

>> [1,2,'a'].join.to_i #=> 12

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