I am fairly new to Ruby and programming and had a couple questions about
if/else and case statements. I was wondering if there were benefits to
using case statements instead of if/elsif/else type statements. Are
case statements faster?
If I am reading in a file line by line and doing something similar to
lines = File.open("file.csv")
FasterCSV.parse(lines) do |row|
if ( lines =~ /^blah/)
puts "blahblahblah"
some_method
end
if ( lines =~ /^name/ && row[1] =="123")
puts "ping pong abc"
another_method
end
if ( lines =~ /^address/ && row[3] =="XYZ")
puts "abcdefghijklmnopqrstuvwxyz"
method3
end
end
Does writing it with a case statement like so benefit me?
lines = File.open("file.csv")
FasterCSV.parse(lines) do |row|
case
when ( lines =~ /^blah/)
puts "blahblahblah"
some_method
when ( lines =~ /^address/ && row[1] =="XYZ")
puts "abcdefghijklmnopqrstuvwxyz"
method3
end
end
While writing this I couldn't figure out how to write my case to be "if
lines begins with"
case "lines =~"
when /^blah/
puts "blahblahblah"
some_method
Lastly is there a "better" way to write an if statement that is
conditional on a bunch of things like
if row[0] == john && row[7] == abc123 && row[8] != nil &&
somehashtable.has_key?(row2)
Case statements are not faster. Both Case and if statements are constant
time operations so there is no speed benefit of one over the other. It
really just comes down to your preference in any given situation. Depending
on the code one or the other can lead to cleaner and easier to understand
code.
Oh and cool name btw
···
On Sat, Jul 10, 2010 at 12:30 AM, John Crichton <a2533488@bofthew.com>wrote:
I am fairly new to Ruby and programming and had a couple questions about
if/else and case statements. I was wondering if there were benefits to
using case statements instead of if/elsif/else type statements. Are
case statements faster?
If I am reading in a file line by line and doing something similar to
lines = File.open("file.csv")
FasterCSV.parse(lines) do |row|
if ( lines =~ /^blah/)
puts "blahblahblah"
some_method
end
if ( lines =~ /^name/ && row[1] =="123")
puts "ping pong abc"
another_method
end
if ( lines =~ /^address/ && row[3] =="XYZ")
puts "abcdefghijklmnopqrstuvwxyz"
method3
end
end
Does writing it with a case statement like so benefit me?
lines = File.open("file.csv")
FasterCSV.parse(lines) do |row|
case
when ( lines =~ /^blah/)
puts "blahblahblah"
some_method
when ( lines =~ /^address/ && row[1] =="XYZ")
puts "abcdefghijklmnopqrstuvwxyz"
method3
end
end
While writing this I couldn't figure out how to write my case to be "if
lines begins with"
case "lines =~"
when /^blah/
puts "blahblahblah"
some_method
Lastly is there a "better" way to write an if statement that is
conditional on a bunch of things like
if row[0] == john && row[7] == abc123 && row[8] != nil &&
somehashtable.has_key?(row2)
I am fairly new to Ruby and programming and had a couple questions about
if/else and case statements. I was wondering if there were benefits to
using case statements instead of if/elsif/else type statements. Are
case statements faster?
If I am reading in a file line by line and doing something similar to
lines = File.open("file.csv")
FasterCSV.parse(lines) do |row|
if ( lines =~ /^blah/)
puts "blahblahblah"
some_method
end
if ( lines =~ /^name/&& row[1] =="123")
puts "ping pong abc"
another_method
end
if ( lines =~ /^address/&& row[3] =="XYZ")
puts "abcdefghijklmnopqrstuvwxyz"
method3
end
end
Does writing it with a case statement like so benefit me?
lines = File.open("file.csv")
FasterCSV.parse(lines) do |row|
case
when ( lines =~ /^blah/)
puts "blahblahblah"
some_method
when ( lines =~ /^address/&& row[1] =="XYZ")
puts "abcdefghijklmnopqrstuvwxyz"
method3
end
end
I personally prefer the case because then it is immediately clear that there is a set of alternatives that belong together. The difference to if elsif else end isn't too big though.
While writing this I couldn't figure out how to write my case to be "if
lines begins with"
case "lines =~"
when /^blah/
puts "blahblahblah"
some_method
I think that has been answered already: since you have more conditions there is no easy alternative to the case form where the condition is in when clause. If you need only a regexp match as only criterion then you can do
case line
when /^blah/
puts "This is a blah line: #{line}"
when /\.$/
puts "This line ends with a dot."
end
Lastly is there a "better" way to write an if statement that is
conditional on a bunch of things like
if row[0] == john&& row[7] == abc123&& row[8] != nil&&
somehashtable.has_key?(row2)
Well, you can encapsulate your condition in something else and use that. Example:
BLAH_LINE = lambda {|line| /^blah/ =~ line && line.length > 87}
class <<BLAH_LINE
alias :=== :
end
case line
when BLAH_LINE
puts "This is it."
...
end
