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Booleans, conditional operators and autoboxing
...time:
E1: `true ? returnsNull() : false` - boolean (auto-unboxing 2nd operand to boolean)
E2: `true ? null : false` - Boolean (autoboxing of 3rd operand to Boolean)
See Java Language Specification, section 15.25 Conditional Operator ? :
For E1, the types of the 2nd and 3rd operands are Boolean...
Is it safe to use -1 to set all bits to true?
...times have surprising behavior because you will have to have the right operand type. Only then you will get the most high value of an unsigned type.
For an example of a possible surprise, consider this one:
unsigned long a = ~0u;
It won't necessarily store a pattern with all bits 1 into a. But ...
Replace all 0 values to NA
...ays in ?'NULL',
NULL represents the null object in R
which is unique and, I guess, can be seen as the most uninformative and empty object.1 Then it becomes not so surprising that
data.frame(x = c(1, NULL, 2))
# x
# 1 1
# 2 2
That is, R does not reserve any space for this null object.2 Mea...
SQL Switch/Case in 'where' clause
...ly below, you formed the SQL incorrectly. I tested mine in SQLServer 2005 and it worked fine.
– Bob Probst
Oct 16 '08 at 0:48
...
What's the difference between lists and tuples?
...cture, lists have order.
Using this distinction makes code more explicit and understandable.
One example would be pairs of page and line number to reference locations in a book, e.g.:
my_location = (42, 11) # page number, line number
You can then use this as a key in a dictionary to store not...
How do I find a “gap” in running counter with SQL?
...n a counter column in an SQL table. For example, if there are values 1,2,4 and 5 I'd like to find out 3.
20 Answers
...
Print all but the first three columns
...$(i-2)=$i; NF=NF-2; print $0}' | tr ' ' '-'
3-4-5-6-7
This is the fixed and parametrized version of larsr solution:
$ echo '1 2 3 4 5 6 7' |
awk '{for(i=n;i<=NF;i++)$(i-(n-1))=$i;NF=NF-(n-1);print $0}' n=4 | tr ' ' '-'
4-5-6-7
All other answers before Sep-2013 are nice but add extra spac...
Django migration strategy for renaming a model and relationship fields
...ome errors if you don't update the names where it's imported e.g. admin.py and even older migration files (!).
Update: As ceasaro mentions, newer versions of Django are usually able to detect and ask if a model is renamed. So try manage.py makemigrations first and then check the migration file.
...
JavaScript function similar to Python range()
...
See this jsfiddle for a proof.
Comparison between range() in JavaScript and Python
It works in the following way:
range(4) returns [0, 1, 2, 3],
range(3,6) returns [3, 4, 5],
range(0,10,2) returns [0, 2, 4, 6, 8],
range(10,0,-1) returns [10, 9, 8, 7, 6, 5, 4, 3, 2, 1],
range(8,2,-2) returns [8...
Is there a difference between copy initialization and direct initialization?
...d require an object to exist).
As examples in our case, in the case of a1 and a2 special rules say that in such declarations, the result object of a prvalue initializer of the same type as a1 is variable a1, and therefore A_factory_func() directly initializes the object a1. Any intermediary functio...