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Is it possible to get element from HashMap by its position?
How to retrieve an element from HashMap by its position, is it possible at all?
14 Answers
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Best way to select random rows PostgreSQL
...arams p
,generate_series(1, 1100) g -- 1000 + buffer
GROUP BY 1 -- trim duplicates
) r
JOIN big USING (id)
LIMIT 1000; -- trim surplus
Generate random numbers in the id space. You have "few gaps", so add 10 % (enough to easil...
How do I update an entity using spring-data-jpa?
...
Identity of entities is defined by their primary keys. Since firstname and lastname are not parts of the primary key, you cannot tell JPA to treat Users with the same firstnames and lastnames as equal if they have different userIds.
So, if you want to upda...
Android Studio: how to remove/update the “Created by” comment added to all new classes?
By default Android Studio automatically adds a header comment to all new classes, e.g.
9 Answers
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Why is rbindlist “better” than rbind?
...w where rbindlist shines are
Fast vectorized merge of list of data.frames by row
Trouble converting long list of data.frames (~1 million) to single data.frame using do.call and ldply
These have benchmarks that show how fast it can be.
rbind.data.frame is slow, for a reason
rbind.data.frame do...
How can I specify a branch/tag when adding a Git submodule?
...ame thing except you can make changes to it.
– deadbabykitten
Feb 2 '16 at 0:13
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How can I escape a double quote inside double quotes?
...hell:
$ echo 'abc'\''abc'
abc'abc
$ echo "abc"\""abc"
abc"abc
It's done by finishing an already-opened one ('), placing the escaped one (\'), and then opening another one (').
Alternatively:
$ echo 'abc'"'"'abc'
abc'abc
$ echo "abc"'"'"abc"
abc"abc
It's done by finishing already opened one ('...
Tricks to manage the available memory in an R session
...of an interactive R session? I use the functions below [based on postings by Petr Pikal and David Hinds to the r-help list in 2004] to list (and/or sort) the largest objects and to occassionally rm() some of them. But by far the most effective solution was ... to run under 64-bit Linux with ample...
Get top n records for each group of grouped results
... for each group:
(
select *
from mytable
where `group` = 1
order by age desc
LIMIT 2
)
UNION ALL
(
select *
from mytable
where `group` = 2
order by age desc
LIMIT 2
)
There are a variety of ways to do this, see this article to determine the best route for your situation:
ht...
Is there a way to access the “previous row” value in a SELECT statement?
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SQL has no built in notion of order, so you need to order by some column for this to be meaningful. Something like this:
select t1.value - t2.value from table t1, table t2
where t1.primaryKey = t2.primaryKey - 1
If you know how to order things but not how to get the previous val...