julia生成一个连续的日期序列 (起始值，年/月/日，系列的

参考文档 链接： A Julia equivalent to Pandas date_range function

function timestamps(start::TimeType, freq::DataType, obs::Int, step::Int=1)
    steps   = freq(step)
    periods = obs * step
    finish  = start + freq(periods - 1)
    collect(start:steps:finish)
end

# start = Date(2000,1,30)
# freq = Day
# lenth = 100
# step = 1 默认的

timestamps(Date(2000,1,30), Day, 100)

100-element Array{Date,1}:
 2000-01-30
 2000-01-31
 2000-02-01
 2000-02-02
 2000-02-03
 2000-02-04
 2000-02-05
 2000-02-06
 2000-02-07
 2000-02-08
 2000-02-09
 2000-02-10
 2000-02-11
 ⋮
 2000-04-27
 2000-04-28
 2000-04-29
 2000-04-30
 2000-05-01
 2000-05-02
 2000-05-03
 2000-05-04
 2000-05-05
 2000-05-06
 2000-05-07
 2000-05-08

# start = Date(2000,1,30)
# freq = Day
# lenth = 100
# step = 2

timestamps(Date(2000,1,30), Day, 100, 2)

100-element Array{Date,1}:
 2000-01-30
 2000-02-01
 2000-02-03
 2000-02-05
 2000-02-07
 2000-02-09
 2000-02-11
 2000-02-13
 2000-02-15
 2000-02-17
 2000-02-19
 2000-02-21
 2000-02-23
 ⋮
 2000-07-24
 2000-07-26
 2000-07-28
 2000-07-30
 2000-08-01
 2000-08-03
 2000-08-05
 2000-08-07
 2000-08-09
 2000-08-11
 2000-08-13
 2000-08-15