大约有 42,000 项符合查询结果（耗时：0.0388秒） [XML]
Why are Where and Select outperforming just Select?
...
Select iterates once over the entire set and, for each item, performs a conditional branch (checking for validity) and a + operation.
Where+Select creates an iterator that skips invalid elements (doesn't yield them), performing a + only on the valid items.
So, the...
Open files in 'rt' and 'wt' modes
Several times here on SO I've seen people using rt and wt modes for reading and writing files.
4 Answers
...
Switch statement: must default be the last case?
...
The C99 standard is not explicit about this, but taking all facts together, it is perfectly valid.
A case and default label are equivalent to a goto label. See 6.8.1 Labeled statements. Especially interesting is 6.8.1.4, which enables...
Exact difference between CharSequence and String in java [duplicate]
...us post . Can any one say what the exact difference between CharSequence and String is, other than the fact that String implements CharSequence and that String is a sequence of character? For example:
...
Extract traceback info from an exception object
...__ attribute that contains the traceback. This attribute is also writable, and can be conveniently set using the with_traceback method of exceptions:
raise Exception("foo occurred").with_traceback(tracebackobj)
These features are minimally described as part of the raise documentation.
All credi...
How to loop through an associative array and get the key? [duplicate]
...
Nobody answered with regular for loop? Sometimes I find it more readable and prefer for over foreach
So here it is:
$array = array('key1' => 'value1', 'key2' => 'value2');
$keys = array_keys($array);
for($i=0; $i < count($keys); ++$i) {
echo $keys[$i] . ' ' . $array[$keys[$i]] . "...
Numpy matrix to array
I am using numpy. I have a matrix with 1 column and N rows and I want to get an array from with N elements.
9 Answers
...
Syntax error on print with Python 3 [duplicate]
... to write it as
print("Hello World")
But if you write this in a program and someone using Python 2.x tries to run it, they will get an error. To avoid this, it is a good practice to import print function:
from __future__ import print_function
Now your code works on both 2.x & 3.x.
Check o...
Extract every nth element of a vector
...eyond the seq solution already mentioned) is to use a short logical vector and use vector recycling:
foo[ c( rep(FALSE, 5), TRUE ) ]
share
|
improve this answer
|
follow
...
CREATE TABLE IF NOT EXISTS equivalent in SQL Server [duplicate]
...
if not exists (select * from sysobjects where name='cars' and xtype='U')
create table cars (
Name varchar(64) not null
)
go
The above will create a table called cars if the table does not already exist.
...