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What does “abstract over” mean?
... (implicit ff: Foldable[F], m: Monoid[B]) =
ff.foldMap(as, f)
Now we have something quite general. The method mapReduce will fold any F[A] given that we can prove that F is foldable and that A is a monoid or can be mapped into one. For example:
case class Sum(value: Int)
case class Pro...
Ruby Bundle Symbol not found: _SSLv2_client_method (LoadError)
...ng homebrew and I somehow managed to break everything. I can't do anything now, this is what I get when I try to do bundle install:
...
What is the difference between “def” and “val” to define a function
...ng var as I need to change it to 3 later
val sq = x*x // evaluates right now
x = 3 // no effect! sq is already evaluated
println(sq)
Surprisingly, this will print 4 and not 9! val (even var) is evaluated immediately and assigned.
Now change val to def.. it will print 9! Def is a function cal...
Does SQLAlchemy have an equivalent of Django's get_or_create?
... new record, it will raise IntegrityError. The whole thing gets messed up, now we don't know what actually happened and we get another error, that no record is found.
– rajat
Oct 8 '15 at 19:31
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Where can I learn how to write C code to speed up slow R functions? [closed]
...t's the best resource for learning how to write C code for use with R? I know about the system and foreign language interfaces section of R extensions, but I find it pretty hard going. What are good resources (both online and offline) for writing C code for use with R?
...
Create list of single item repeated N times
...'string'] * len(columns)
Mutable items
I've used Python for a long time now, and I have never seen a use-case where I would do the above with a mutable instance. Instead, to get, say, a mutable empty list, set, or dict, you should do something like this:
list_of_lists = [[] for _ in columns]
T...
Is explicitly closing files important?
...ot good practice to leave your files open. In fact, in cpython 3 you will now get warnings that the system had to close files for you if you didn't do it.
Moral: Clean up after yourself. :)
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Comparing date part only without comparing time in JavaScript
...nds and milliseconds on date1 do the following:
date1.setHours(0,0,0,0)
Now you can compare the two dates as DATES only without worrying about time elements.
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Serializing PHP object to JSON
...ion >= 5.4, do not use this answer, and just use PHP>= 5.4 (or, you know, a recent one) and implement the JsonSerializable interface
You would define a function, for instance named getJsonData();, which would return either an array, stdClass object, or some other object with visible paramet...
Linux command to print directory structure in the form of a tree
...g' -e 's/─/├/' -e '$s/├/└/'
This is much like the output of tree now:
.
├─pkcs11
├─pki
├───ca-trust
├─────extracted
├───────java
├───────openssl
├───────pem
├─────source
├───────anchors...