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Find size of an array in Perl
...dard way to get an array's size.
The second way actually returns the last index of the array, which is not (usually) the same as the array size.
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How to convert SQL Query result to PANDAS Data Structure?
... way to do it, as you don't need to manually use .keys() to get the column index. Probably Daniel's answer was written before this method existed. You can also use pandas.io.sql.read_frame()
– RobinL
Oct 13 '13 at 13:54
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How to find a hash key containing a matching value
....9 and greater:
hash.key(value) => key
Ruby 1.8:
You could use hash.index
hsh.index(value) => key
Returns the key for a given value. If
not found, returns nil.
h = { "a" => 100, "b" => 200 }
h.index(200) #=> "b"
h.index(999) #=> nil
So to get "oran...
Rails 3: Get Random Record
... big tables but more sql-style
UPD. You can use the following trick on an indexed column (PostgreSQL syntax):
select *
from my_table
where id >= trunc(
random() * (select max(id) from my_table) + 1
)
order by id
limit 1;
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How do you divide each element in a list by an int?
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@Casa: Someone tested this at stackoverflow.com/q/1247490 . The conclusion seems to be that list comprehensions win, in this particular case.
– Brian
Nov 23 '11 at 16:15
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How to use the 'main' parameter in package.json?
...meter in your package.json if the entry point to your package differs from index.js in its root folder. For example, people often put the entry point to lib/index.js or lib/<packagename>.js, in this case the corresponding script must be described as main in package.json.
You can't have two scr...
How to find and return a duplicate value in array
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Simply find the first instance where the index of the object (counting from the left) does not equal the index of the object (counting from the right).
arr.detect {|e| arr.rindex(e) != arr.index(e) }
If there are no duplicates, the return value will be nil.
I be...
How do I modify fields inside the new PostgreSQL JSON datatype?
... create_missing boolean default true)
path can contain JSON array indexes too & negative integers that appear there count from the end of JSON arrays. However, a non-existing, but positive JSON array index will append the element to the end of the array:
SELECT jsonb_set('{"a":[null,{"b...
How can I make SQL case sensitive string comparison on MySQL?
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@adjwilli If the column was a part of an index, you will suffer a performance hit on queries reliant on that index. To maintain performance, you need to actually alter the table.
– dshin
Sep 19 '13 at 18:50
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MySQL order by before group by
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For scaling, the compound INDEX(post_author, post_date) is important.
– Rick James
Mar 1 '15 at 16:08
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