How to create ISO Date String

It is a more and more common task that we need to have a date or maybe date with time as String.

There are two reasonable ways to do this:
* We may want the date formatted in the users Locale, whatever that is.
* We want to use a generic date format, that is for a broader audience or for usage in data exchange formats, log files etc.

The first issue is interesting, because it is not always trivial to teach the software to get the right locale and to use it properly… The mechanisms are there and they are often used correctly, but more often this is just working fine for the locale that the software developers where asked to support.

So now the question is, how do we get the ISO-date of today in different environments.

Linux/Unix-Shell (bash, tcsh, …)

date "+%F"

TeX/LaTeX


\def\dayiso{\ifcase\day \or
01\or 02\or 03\or 04\or 05\or 06\or 07\or 08\or 09\or 10\or% 1..10
11\or 12\or 13\or 14\or 15\or 16\or 17\or 18\or 19\or 20\or% 11..20
21\or 22\or 23\or 24\or 25\or 26\or 27\or 28\or 29\or 30\or% 21..30
31\fi}
\def\monthiso{\ifcase\month \or
01\or 02\or 03\or 04\or 05\or 06\or 07\or 08\or 09\or 10\or 11\or 12\fi}
\def\dateiso{\def\today{\number\year-\monthiso-\dayiso}}
\def\todayiso{\number\year-\monthiso-\dayiso}

This can go into a file isodate.sty which can then be included by \include or \input Then using \todayiso in your TeX document will use the current date. To be more precise, it is the date when TeX or LaTeX is called to process the file. This is what I use for my paper letters.

LaTeX

(From Fritz Zaucker, see his comment below):

\usepackage{isodate} % load package
\isodate % switch to ISO format
\today % print date according to current format

Oracle


SELECT TO_CHAR(SYSDATE, 'YYYY-MM-DD') FROM DUAL;

On Oracle Docs this function is documented.
It can be chosen as a default using ALTER SESSION for the whole session. Or in SQL-developer it can be configured. Then it is ok to just call

SELECT SYSDATE FROM DUAL;

Btw. Oracle allows to add numbers to dates. These are days. Use fractions of a day to add hours or minutes.

PostreSQL

(From Fritz Zaucker, see his comment):

select current_date;
—> 2016-01-08


select now();
—> 2016-01-08 14:37:55.701079+01

Emacs

In Emacs I like to have the current Date immediately:

(defun insert-current-date ()
"inserts the current date"
(interactive)
(insert
(let ((x (current-time-string)))
(concat (substring x 20 24)
"-"
(cdr (assoc (substring x 4 7)
cmode-month-alist))
"-"
(let ((y (substring x 8 9)))
(if (string= y " ") "0" y))
(substring x 9 10)))))
(global-set-key [S-f5] 'insert-current-date)

Pressing Shift-F5 will put the current date into the cursor position, mostly as if it had been typed.

Emacs (better Variant)

(From Thomas, see his comment below):

(defun insert-current-date ()
"Insert current date."
(interactive)
(insert (format-time-string "%Y-%m-%d")))

Perl

In the Perl programming language we can use a command line call

perl -e 'use POSIX qw/strftime/;print strftime("%F", localtime()), "\n"'

or to use it in larger programms

use POSIX qw/strftime/;
my $isodate_of_today = strftime("%F", localtime());

I am not sure, if this works on MS-Windows as well, but Linux-, Unix- and MacOS-X-users should see this working.

If someone has tried it on Windows, I will be interested to hear about it…
Maybe I will try it out myself…

Perl 5 (second suggestion)

(From Fritz Zaucker, see his comment below):

perl -e 'use DateTime; use 5.10.0; say DateTime->now->strftime(„%F“);‘

Perl 6

(From Fritz Zaucker, see his comment below):

say Date.today;

or

Date.today.say;

Ruby

This is even more elegant than Perl:

ruby -e 'puts Time.new.strftime("%F")'

will do it on the command line.
Or if you like to use it in your Ruby program, just use

d = Time.new
s = d.strftime("%F")

Btw. like in Oracle SQL it is possible add numbers to this. In case of Ruby, you are adding seconds.

It is slightly confusing that Ruby has two different types, Date and Time. Not quite as confusing as Java, but still…
Time is ok for this purpose.

C on Linux / Posix / Unix


#include
#include
#include

main(int argc, char **argv) {

char s[12];
time_t seconds_since_1970 = time(NULL);
struct tm local;
struct tm gmt;
localtime_r(&seconds_since_1970, &local);
gmtime_r(&seconds_since_1970, &gmt);
size_t l1 = strftime(s, 11, "%Y-%m-%d", &local);
printf("local:\t%s\n", s);
size_t l2 = strftime(s, 11, "%Y-%m-%d", &gmt);
printf("gmt:\t%s\n", s);
exit(0);
}

This speeks for itself..
But if you like to know: time() gets the seconds since 1970 as some kind of integer.
localtime_r or gmtime_r convert it into a structur, that has seconds, minutes etc as separate fields.
stftime formats it. Depending on your C it is also possible to use %F.

Scala


import java.util.Date
import java.text.SimpleDateFormat
...
val s : String = new SimpleDateFormat("YYYY-MM-dd").format(new Date())

This uses the ugly Java-7-libraries. We want to go to Java 8 or use Joda time and a wrapper for Scala.

Java 7


import java.util.Date
import java.text.SimpleDateFormat

...
String s = new SimpleDateFormat("YYYY-MM-dd").format(new Date());

Please observe that SimpleDateFormat is not thread safe. So do one of the following:
* initialize it each time with new
* make sure you run only single threaded, forever
* use EJB and have the format as instance variable in a stateless session bean
* protect it with synchronized
* protect it with locks
* make it a thread local variable

In Java 8 or Java 7 with Joda time this is better. And the toString()-method should have ISO8601 as default, but off course including the time part.

Summary

This is quite easy to achieve in many environments.
I could provide more, but maybe I leave this to you in the comments section.
What could be interesting:
* better ways for the ones that I have provided
* other databases
* other editors (vim, sublime, eclipse, idea,…)
* Office packages (Libreoffice and MS-Office)
* C#
* F#
* Clojure
* C on MS-Windows
* Perl and Ruby on MS-Windows
* Java 8
* Scala using better libraries than the Java-7-library for this
* Java using better libraries than the Java-7-library for this
* C++
* PHP
* Python
* Cobol
* JavaScript
* …
If you provide a reasonable solution I will make it part of the article with a reference…
See also Date Formats

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Scala Exchange 2015

It was possible to arrange a visit of Scala Exchange 2015 in London, short #ScalaX.

I visited the following events:

Scala Exchange 2014

Deutsch

I have been visiting the conference Scala eXchange ( #scalaX ) organized by Skillsmatter in London.

Here is some information about the talks that I have attended and the highlights:

The Binary Compatibility Challenge

Martin Odersky

Examples can be constructed for each of the four combinations of binary and source code compatibility.
We wish more of both. The talk is mostly about binary compatibility.
For Scala the conflict is innovation vs compatibility. Java chose one extreme to retain compatibility at any cost, which is considered more like a constraint then a restriction by the Java developers. It is easier for them because they control the JVM which is again close to the Java language. Clojure, Ruby, JRuby, Perl, Python, PHP and some others have less problems with this issue because the software is distributed as source code and compiled when run, just in time.
Reproducible builds are hard to achieve in Scala, just think of the many build tools like ivy, gradle, maven, sbt, ant, make (yes, I have seen it),…
The idea is to split the around 30 steps of compilation of scala into two groups. The first group could yield an intermediate format after around 10 internal compilation steps, which might be stored as tree of the program in a clever binary format. This could be a good compromise and address some of the issues, if kept stable. More likely will programs be combinable compatibly with this format than with binary or source only. It would also save time during compilation, which is a desirable improvement for scala.

REST on Akka: Connect to the world

Mathias Doenitz

Akka-http is the spray 2.0 or successor of spray. It follows the lines of spray, but improves on some of the shortcomings.
It should be used for reactive streams in Akka and is important enough to be part of core Akka.
TCP-flow-control can be used to implement „back pressure“.

Bootstrapping the Scala.js Ecosystem

Haoyi Li

Scala shall be compiled to as second alternative instead of JVM. The target is the browser, not so much server side JavaScript, where the JVM is available and better.
Advantage for applications: Some code can be used on both sides, for example HTML-tag-generation, validation etc. This is more elegant than using two languages. Also Scala might be considered a more sane language for the browser than JavaScript, although JavaScript is not such a bad language, but suffers like PHP and VBA from being used by non-developers who come from web design side and try a little JavaScript as part of their work, tripping into each of the pitfalls that we developers have already had some time ago when we had our first experience.
Libraries prove to be hard. They are huge and it is hard to transfer them. Optimization is needed to deal with this, like for Android development.
Reflection is not available on scala.js. Many things do not work because of that, but enough things to make it useful do work.
Serialization is another challenge, because many frameworks rely on reflection, but there seems to be a solution for that.
Integer types are a little bit crappy. JS only has double which can do 53 bit integers. Long has to be built from two doubles.

Introduction to Lambda Calculus

Maciek Makowski

Very theoretical talk. Lamba calculus is pure math or even more theoretical, pure theoretical informatics, but it can be made a complete programming language with some thinking. It can be used for dealing with issues like computability. Many nice proofs are possible. The theoretical essence of functional programming languages is there. Some key words: „Church Rosser Theorem“, „Programming with Lambda-Calculus“, „numbers as lambda expressions“ (church encoding), „y combinator“, „fixed point combinator“, „lambda cube“, „fourth dimension for Subtypes“, ….
Very small language, great for proofs, not relevant or applicable for practical purposes.

State of the Typelevel

Lars Hupel

Typelevel is inpired by Haskell. Libraries by them are scalaz, shapeless, spire, scalaz-stream, monocle and more.
We should strive to get correct programs and optimize where the needs arises.
The JVM integers are not good. Think of the silent overflow. Floats (float and double) are good for numerical mathematicians and scientists with knowledge in this area, who can deal with error propagation an numerical inaccuracy.
Off course numbers can be seen as functions, like this:
$x=f(.)$ mit $\bigwedge_{n \in \Bbb N: n>0} \frac{f(n)-1}{n} < x < \frac{f(n)+1}{n}$ Equality of real numbers cannot be decided in finite time. What is "Costate command coalgebra"? Monocle provides "lenses" and similar stuff known from Haskell... Good binary serialization formats are rare in the JVM world. How should the fear of scalaZ and monads be overcome? Remember: "A monad is a monoid in the category of endofunctors. So what is the problem?" as could be read on Bodil Stokke’s T-shirt.

Slick: Bringing Scala’s Powerful Features to Your Database Access

Rebecca Grenier

Slick is a library that generates and executes SQL queries. The conceptional weaknesses of JPA and Hibernate are avoided.
It has drivers for the five major DBs (PostgreSQL, mySQL/mariaDB, Oracle, MS-SQL-Server and DB2) and some minor DBs, but it is not free for the three commercial DBs.
Inner and outer joins are possible and can be written in a decent way.
With database dictionaries slick is now even able to generate code. Which I have done, btw. a lot using Perl scripts running on the DDL-SQL-script. But this is better, off course…

Upcoming in Slick 2.2

Jan Christopher Vogt

Monads haunt us everywhere, even here. Time to learn what they are. I will be giving a talk in the Ruby-on-Rails user group in Zürich, which will force me to learn it.
Here they come: monadic sessions….
Sessions in conjunction with futures are the best guarantee for all kinds of nightmares, because the SQL is sometimes executed when the session is no longer valid or the transaction is already over. When dealing with transactional databases a lot of cool programming patterns become harder. Just think of the cool java guys who execute stuff by letting a EJB-method return an instance of an inner class with the DB-session implicitely included there and calling a method which via JPA indirectly and implicitely does DB-access long after the EJB-method is over. Have fun when debugging this stuff. But we know about it and address it here.
At least Slick is theoretically correct, other than JPA which I conject to be theoretically incorrect, apart from the shortcomings of the concrete implementations.
Several statements can be combined with andThen or a for-comprehension. Be careful, by default this uses separate sessions and transactions, with very funny effects. But threads and sessions are expensive and must not be withheld during non-running non-SQL-activities by default. Reactiveness is so important. Futures and thread pools look promising, but this fails miserably when we have blocking operations involved, that will occupy our threads for nothing.
We would like to have assynchronous SQL-access, which can be done on DB- and OS-level, but JDBC cannot. So we have to work around on top of JDBC. Apart from using a reasonably low number of additional threads this approach seems to be viable.
Statically type checked SQL becomes possible in the future.

No more Regular Expressions

Phil Wills

I love the regex of Perl. Really. So why do effort to give up something so cool, even in non-perl-languages?
It is not as bad as it sounds. We retain regular expressions as a concept, just do not call them like that (for marketing reasons I assume) and write them differently. Writing them as strings between // is very natural in Perl, but it breaks the flow of the language in Scala. A typical programmatical scala-like approach is more natural and more type safe. And more robust in case of errors. org.paraboiled2 can be used. Capture is unfortunately positional, unlike in newer Perl-regex, where captures can be named. But it hurts less here.

Scala eXchange – Q&A Panel

Jon Pretty, Kingsley Davies, Lars Hupel, Martin Odersky, and Miles Sabin

Interesting discussions…

Why Scala is Taking Over the Big Data World

Dean Wampler

‚“Hadoop“ is the „EJB“ of our time.‘
MapReduce is conceptionally already functional programming. So why use Java and not Scala?
Some keywords: „Scalding“, „Storm“, „Summing bird“, „Spark“.
Scala can be more performant than python, which is so popular in this area, but migration has to be done carefully.

Case classes a la carte with shapeless, now!

Miles Sabin

Example: tree structure with backlinks. Hard to do in strict immutabilty. Shapeless helps.

Reactive Programming with Algebra

André Van Delft

Algebra can be fun and useful for programming. Algebraic interpretations were introduced.
Page is subscript-lang.org.
Algebra of communicationg processes. It is very powerful and can even be applied to other targets, for example operation of railroad systems.
Every program that deals with inpout is in its way a parser. So ideas from yacc and bison apply to them.

High Performance Linear Algebra in Scala

Sam Halliday

Lineare Algebra has been addressed extremely well already, so the wheel should not be reinvented.
TL;D, Netflix and Breeze.
Example for usage of that stuff: Kalman Filter.
netlib has reference implementation in Fortran, a well defined interface and a reliable set of automatic tests. How do we take this into the scala world?
Fortran with C-Wrapper for JNI. (cblas)
compile Fortran to Java. really.
Alternate implementations of the same test suite in C.
High-Performance is not only about speed and memory alone, but about those under the given requirements concerning correctness, precision and stability.
Hardware is very interesting. The CPU-manufacturers are talking with the netlib team.
Can GPU be used? Off course, but some difficulties are involved, for example transfer of data.
FPGA? maybe soon? Or something like GPU, without graphics and operating on the normal RAM?
We will see such stuff working in the future.

An invitation to functional programming

Rúnar Bjarnason

Referential transparency, something like compatibility with the memoize pattern.
Pure functions…
Parallelization..
Comprehensiveness.. The all time promise, will it be kept this time?
Functional programming is not good for the trenches of real life project, but for getting out of the trenches. This should be our dream. Make love not war, get rid of trenches…

Building a Secure Distributed Social Web using Scala & Scala-JS

Henry Story

Spargl is like SQL for the „semantic web“.
Developed with support from Oracle.
We can have relativiity of of truth while retaining the absolute truth. The speech was quite philosophical, in a good way.
Graphs can be isomorphic, but have a different level of trust, depending on where the copy lies.
Linked data protocol becomes useful.
How is spam and abuse avoided? WebID?
We are not dealing with „Big Data“ but with massively parallel and distributed „small data“.

TableDiff – a library for showing the difference between the data in 2 tables

Sue Carter

What is the right semantics for a diff?
What do we want to see? How are numbers and strings compared when occurring in fields?
Leave timestamps that obviously differ but do not carry much information out.

Evolving Identifiers and Total Maps

Patrick Premont

Idea is to have a map where get always returns something non-null. Smart type concepts avoid the compilation of a get call that would not return something.
Very interesting idea, but I find it more useful as theoretical concept rather than for practical purposes. The overhead seems to be big.

Summary

Overall it was a great conference.

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Scala Exchange 2013

Deutsch

I have visited the conference ScalaX 2013 in London on the beginning of December.

It was really fun. The talks were quite challenging, maybe even a little bit more than on other conferences I have visited, but that was really fun to listen to. About 400 participants were there and three tracks were available. So it was possible to learn a lot about advanced concepts in functional programming and software architecture with a focus on Scala, but also some Haskell and Clojure.

Some interesting talks were:

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