Extracting Dates

Community Support
1

Hi,

I have written a function which allows me to return the number of Sundays between any two given dates, i.e. f[firsdate; last date] which is run for the year 2014: f[2014.01.01; 2014.12.31] returns a value of 52 (There were 52 Sundays in 2014). I am wondering if there is a way that I can only count Sundays which fell on the first of any given month of any year? For example, in 2014 this happened once.

Thanks.

2

q){(“d”$(“m”$x)+til 12)inter a where 1=mod[;7]a:x+til 1+y-x}[2014.01.01;2014.12.31]

,2014.06.01

You can put a count in there if you just want the count.

Terry

3

Hi,

Firstly I’d suggest counting the number of first of the months which are Sundays, rather than vice versa, as it will require fewer checks. You could use the following function:

{[sd;ed] sm:month$sd;em:month$ed;sum 1=mod[;7]`date$sm+til 1+em-sm}[2014.01.01;2014.12.31]

This function casts the start and end date to months, generates a list of intervening months, then casts back to dates (casting a month to a date automatically chooses the first day of the month). It then uses mod to check which day the resulting dates are (0 - Saturday, etc) and checks which are Sundays, summing the result for the count.

Regards,

Sam

From: personal-kdbplus@googlegroups.com <personal-kdbplus@googlegroups.com> on behalf of Diarmaid Doherty <diarmaid-doherty@hotmail.com>
Sent: 12 June 2019 15:10:20
To: Kdb+ Personal Developers
Subject: [personal kdb+] Extracting Dates
 

Hi,

I have written a function which allows me to return the number of Sundays between any two given dates, i.e. f[firsdate; last date] which is run for the year 2014: f[2014.01.01; 2014.12.31] returns a value of 52 (There were 52 Sundays in 2014). I am wondering if there is a way that I can only count Sundays which fell on the first of any given month of any year? For example, in 2014 this happened once.

Thanks.

–
Submitted via Google Groups

4

It’d be much easier to perform the checks in reversed order, i.e., check among the first days of each month for Sundays. The code below demonstrates this:

f:{[begin;end] sum 1=mod[;7]date${x+1+til y-x}.month$(begin;end) }