Ruby学习中，对这几个方法用法记下。

# map 针对每个element进行变换并返回整个修改后的数组
def map_method
  arr1 = ["name2", "class2"]
  arr1.map {|num| num + "and"}
  print "map ====",arr1, "\n"
end

def map1_method
  arr1 = ["name2", "class2"]
  arr1.map! {|num| num + "and"}
  print "map! ==== ", arr1, "\n"
end

def map2_method
  arr1 = ["name3", "class3"]
  # &:表示item
  arr2 = arr1.map(&:upcase)
  print "map2 ====", arr2, "\n"
end
# reduce  把array变换为一个值后返回
def reduce_method
  arr1 = ["a", "b", "c", "d"]
  arr2 = arr1.reduce(:+)
  print "reduce ====", arr1, "\n"
  print "reduce ====", arr2, "\n"
end

def reduce_method2
  sum1 = (1..100).reduce(:+)
  sum2 = (1..100).reduce(0) do |sum, value|
    sum + value
  end
  print "reduce sum1 ====#{sum1}\n"
  print "reduce sum2 ====#{sum2}\n"
end

# select 根据条件返回一个子集
def select_method
  arr = (1..8).select {|x| x % 2 == 0}
  print "select ====", arr, "\n"
end

#reject 根据条件提出一个子集
def reject_method
  arr = (1..8).reject {|x| x % 2 == 0}
  print "reject ====", arr, "\n"

end

#each 遍历数组每个元素，但不生成新的数组
def each_method
  arr1 = ["name2", "class2"]
  arr2 = arr1.each {|num| num + "and"}
  print "each ====", arr2, "\n"
end

#collect 同map一样，collect!同map!一样
def collect_method
  arr1 = ["name2", "clas2"]
  arr2 = arr1.collect { |num| num + "and" }
  print "collect ====", arr2, "\n"
end

map_method
map1_method
map2_method
reduce_method
select_method
reject_method
each_method
collect_method
reduce_method2