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std::shared_ptr thread safety explained
I'm reading http://gcc.gnu.org/onlinedocs/libstdc++/manual/shared_ptr.html and some thread safety issues are still not clear for me:
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What is the recommended way to delete a large number of items from DynamoDB?
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What I ideally want to do is call LogTable.DeleteItem(user_id) -
Without supplying the range, and have it delete everything for me.
An understandable request indeed; I can imagine advanced operations like these might get added over time by the AWS team (they have a history of st...
Mean per group in a data.frame [duplicate]
... object. It’s easier to do what you’re after with dplyr: d %>% group_by(Name) %>% mutate(mean1=mean(Rate1), mean2=mean(Rate2))
– jbaums
May 29 '19 at 9:48
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Comparing date part only without comparing time in JavaScript
...ne offset, or is already UTC, just keep the date part, reflecting the date _in that timezone_
if(typeof initDate === "string" && initDate.match(/((\+|-)\d{2}:\d{2}|Z)$/gm)){
utcMidnightDateObj = new Date( initDate.substring(0,10) + 'T00:00:00Z');
} else {
// if init date is no...
Bash set +x without it being printed
...ution to this just recently when I became annoyed with it:
shopt -s expand_aliases
_xtrace() {
case $1 in
on) set -x ;;
off) set +x ;;
esac
}
alias xtrace='{ _xtrace $(cat); } 2>/dev/null <<<'
This allows you to enable and disable xtrace as in the following, wh...
Argparse optional positional arguments?
...se nargs='?' (or nargs='*' if you will need more than one dir)
parser.add_argument('dir', nargs='?', default=os.getcwd())
extended example:
>>> import os, argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('-v', action='store_true')
_StoreTrueActi...
Split list into multiple lists with fixed number of elements
...st[List[X]] =
if (xs.size <= n) xs :: Nil
else (xs.splitAt(n)._1) :: split(n,xs.splitAt(n)._2)
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What is Weak Head Normal Form?
...es for an expression to be in WHNF:
A constructor: constructor expression_1 expression_2 ...
A built-in function with too few arguments, like (+) 2 or sqrt
A lambda-expression: \x -> expression
In other words, the head of the expression (i.e. the outermost function application) cannot be eval...
Naming of ID columns in database tables
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ID is a SQL Antipattern.
See http://www.amazon.com/s/ref=nb_sb_ss_i_1_5?url=search-alias%3Dstripbooks&field-keywords=sql+antipatterns&sprefix=sql+a
If you have many tables with ID as the id you are making reporting that much more difficult. It obscures meaning and makes comp...
Time complexity of Sieve of Eratosthenes algorithm
...cause we need an array of n elements in any case?
– a_123
Mar 25 '16 at 21:35
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