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Quickly reading very large tables as dataframes
...
# sqldf as on SO
f <- file("test.csv")
system.time(SQLf <- sqldf("select * from f", dbname = tempfile(), file.format = list(header = T, row.names = F)))
## user system elapsed
## 10.21 0.47 10.73
ff / ffdf
require(ff)
system.time(FFDF <- read.csv.ffdf(file="test.csv",nro...
Disabling Chrome cache for website development
...ck (or hold left click) on the reload button at the top of the browser and select "Empty Cache and Hard Reload."
This will go beyond "Hard Reload" to empty the cache entirely, ensuring that anything downloaded via javascript or etc. will also avoid using the cache. You don't have to mess with set...
Struct Constructor in C++?
...s.
struct blocknode
{
unsigned int bsize;
bool free;
unsigned char *bptr;
blocknode *next;
blocknode *prev;
blocknode(unsigned int sz, unsigned char *b, bool f = true,
blocknode *p = 0, blocknode *n = 0) :
bsize(sz), free(f), bptr(b), prev(p), ne...
Number of rows affected by an UPDATE in PL/SQL
... block, this can be achieved.
... If anyone has a solution to use it in a SELECT Command, I would be interested.
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Unique random string generation
...ncat(
Enumerable
.Repeat(0, int.MaxValue)
.Select(e => RandomByte())
.Where(randomByte => randomByte < outOfRange)
.Take(length)
.Select(randomByte => alphabet[randomByte % alphabet.Length])
);
}
byte RandomByte()
{...
Split comma-separated strings in a column into separate rows
... occasions, because the datatable approaches only produce tables with the "selected" columns, while dplyr produces a result with all the columns (including the ones not involved in the analysis and without having to write their names in the function).
– Ferroao
...
Reading a string with scanf
...tring[0]). On the other hand, scanf("%s", &string) passes a pointer-to-char[256], but it points to the same place.
Then scanf, when processing the tail of its argument list, will try to pull out a char *. That's the Right Thing when you've passed in string or &string[0], but when you've pas...
What exactly is nullptr?
...rloading a function for both pointers and integers, and passing nullptr to select the pointer version. Passing NULL or 0 would confusingly select the int version.
A cast of nullptr_t to an integral type needs a reinterpret_cast, and has the same semantics as a cast of (void*)0 to an integral type (...
What's the difference between utf8_general_ci and utf8_unicode_ci?
...or "ǽ" == "æ". For sorting this makes sense but could be surprising when selecting via equalities or dealing with unique indices - bugs.mysql.com/bug.php?id=16526
– Mat Schaffer
Mar 13 '15 at 15:22
...
SQL: deleting tables with prefix
...r you:
In the MySQL shell or through PHPMyAdmin, use the following query
SELECT CONCAT( 'DROP TABLE ', GROUP_CONCAT(table_name) , ';' )
AS statement FROM information_schema.tables
WHERE table_name LIKE 'myprefix_%';
This will generate a DROP statement which you can than copy and execut...