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Reshape three column data frame to matrix (“long” to “wide” format) [duplicate]
...y ways to do this. This answer starts with what is quickly becoming the standard method, but also includes older methods and various other methods from answers to similar questions scattered around this site.
tmp <- data.frame(x=gl(2,3, labels=letters[24:25]),
y=gl(3,1,6, labe...
scp or sftp copy multiple files with single command
...te server in different directories.
For example, I want to run these 4 commands at once.
15 Answers
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Is storing a delimited list in a database column really that bad?
...y connection with the authors. I like to celebrate good products, services and help when I see it.
– therobyouknow
Jan 30 '12 at 16:22
2
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How to permanently remove few commits from remote branch
...You git reset --hard your local branch to remove changes from working tree and index, and you git push --force your revised local branch to the remote. (other solution here, involving deleting the remote branch, and re-pushing it)
This SO answer illustrates the danger of such a command, especially ...
Check whether variable is number or string in JavaScript
...
If you're dealing with literal notation, and not constructors, you can use typeof:.
typeof "Hello World"; // string
typeof 123; // number
If you're creating numbers and strings via a constructor, such as var foo = new String("foo"), you should keep in m...
How to check if an object is a generator object in python?
...ance(gen, (types.GeneratorType, map, filter)) is useful to also detect map and filter. This will still not include other iterables and iterators though.
– jlh
May 2 at 14:32
a...
Difference between a theta join, equijoin and natural join
I'm having trouble understanding relational algebra when it comes to theta joins, equijoins and natural joins. Could someone please help me better understand it? If I use the = sign on a theta join is it exactly the same as just using a natural join?
...
How can I wait for set of asynchronous callback functions?
...h your code, so I'll make up a scenario. Let's say you have 10 ajax calls and you want to accumulate the results from those 10 ajax calls and then when they have all completed you want to do something. You can do it like this by accumulating the data in an array and keeping track of when the last ...
Can't escape the backslash with regex?
...tring parser will remove two of them when "de-escaping" it for the string, and then the regex needs two for an escaped regex backslash).
For instance:
regex("\\\\")
is interpreted as...
regex("\\" [escaped backslash] followed by "\\" [escaped backslash])
is interpreted as...
regex(\\)
is i...
Best way to test if a row exists in a MySQL table
...ou could also try EXISTS:
SELECT EXISTS(SELECT * FROM table1 WHERE ...)
and per the documentation, you can SELECT anything.
Traditionally, an EXISTS subquery starts with SELECT *, but it could
begin with SELECT 5 or SELECT column1 or anything at all. MySQL
ignores the SELECT list in such ...