Code Block Syntax
values.each { |x| print x } # Single line statement
values.each { |x| # {}: Multiple line block
print x
}
values.each do |x| # do end: multiple line block
print x
end
Ruby Numeric Enumerator
0.upto(9) {|x| print x} # From 0 up to 9: 0123456789
3.times {|x| print x} # 3 iterations: 012
0.step(1, 0.1) do |x|
print x # From 0 to 1 with step 0.1: 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
end
Ruby equivalent of the for loop "for (i=0; i<count; i++)"
count = 5
0.upto(count) do |x|
puts x
end
Ruby Collection Enumerator
Iterate through each Ruby object elements: each
[1,2,3].each {|x| print x } # 123
(1..3).each {|x| print x } # 123
{:one=> 'a', :two=> 'b'}.each do |key,value| # two-b one-a
print "#{key}-#{value} "
end
Iterate through Ruby object elements and return a collection of derived values: map/collect
square = [1,2,3].collect {|x| x*x} # [1,4,9]
square = [1,2,3].map {|x| x*x} # [1,4,9]
words = ["hello", "world"]
result = words.map {|x| x.upcase } # ["HELLO", "WORLD"]
Return an object with selected or rejected Ruby elements: select/reject
even = (1..10).select {|x| x%2 == 0} # [2,4,6,8,10]
odd = (1..10).reject {|x| x%2 == 0} # [1,3,5,7,9]
Apply an aggregate functions to all Ruby object elements
data = [1, 2, 3]
total = data.inject {|sum, x| sum + x } # 1+2+3=6
prod = data.inject(1.0) {|p,x| p*x } # 1.0*1*2*3 = 6
maximum = data.inject do |max,x|
max>x ? max : x # 3
end
sum = 0
[1, 2, 3].each {|x| sum += x }
puts sum # 6
Local variables (Ruby 1.9)
# Separate parameters |x;y| with ";" declare the variables local to the block only
x = 0
[1, 2, 3].each {|x;y| x += y}
puts x # 0
Merge 2 Ruby object elements/collection: zip
(1..3).zip([4,5,6]) {|x| print x.inspect } # zip merge top elements of the 2 objects and return as x
# Prints "[1,4][2,5][3,6]"
Ruby File Enumerator
File.open(filename) do |f|
f.each {|line| print line } # Loop and print each line until eof
end
File.open(filename) do |f|
f.each_with_index do |line, number| # Each line and it's line number
print "#{number}: #{line}"
end
end
Implement Custom Enumerator
Call a caller code block n times
def sqLoop(n)
while n > 0 do
yield n, n*n # Call the code block with 2 parameters
n = n - 1
end
end
Call enumerator
sqLoop(5) {|x,y| print x, "-", y, " "} # 5-25 4-16 3-9 2-4 1-1
Find the maximum of a collection
def find_max(v)
length = v.length
max = v[0]
current = 1
while current < length do
max = yield max, v[current] # Call the code block to see which is larger
current += 1
end
max
end
data = [4, 5, 2, 9, 4]
max = find_max(data) {|m,x| m>x ? m : x } # 9
Support a caller with or without a code block
def find_max(v)
length = v.length
max = v[0]
current = 1
while current < length do
if (block_given?) # If the caller supply a code block
max = yield max, v[current] if block_given?
else # If the caller has no code block
max = max > v[current] ? max : v[current]
end
current += 1
end
max
end
max1 = find_max(data) {|m,x| m>x ? m : x }
max2 = find_max(data) # Call without a code block
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