This puts leading zeros with 8!:2

'q<->5.0,q<->r<0>3.0,r<0>2.0' 8!:2[1942 9 2

1942-09-02

-----Original Message-----
From: Programming <[email protected]> On Behalf Of Joe 
Bogner
Sent: Wednesday, April 4, 2018 16:56
To: [email protected]
Subject: [Jprogramming] converting date number to iso 8601

I'm curious if there is a speedier way to convert a date stored as a number 
like 20180101 or 20170228 to the ISO 8601 equivalent:

This does OK

   datenumToISO =: 3 : 0
(4&{. , '-' , 2&{.@(4&}.) , '-' , _2&{.)"1 ": y
)

datenumToISO 20180101
2018-01-01
   datenumToISO 20180228
2018-02-28


But is slower than I'd like ... no big deal but just curious

6!:2 'datenumToISO (5e6 1 $ 20180102)'
4.29083

sprintf is slow

dateNumToISO2 =: 3 : 0
'%d-%02d-%02d' sprintf ,:(0 100 100 #: y)
)

   (6!:2) 'dateNumToISO2 (1e5 # 20180102)'
2.34002
   (6!:2) 'dateNumToISO2 (1e6 # 20180102)'
25.4977


8!:2 shows promise but I can't figure out the formatting string to add a 
leading zero if it's possible

(6!:2) '8!:2 (0 100 100 #: (5e6 # 20180102))'
1.4853

'q<->,q<->,d' 8!:2 (0 100 100 #: (1 # 20180102))
2018-1-2
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