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Linux: copy and create destination dir if it does not exist
...ating any
missing intermediate directories.
Example:
/tmp $ mkdir foo
/tmp $ mkdir foo/foo
/tmp $ touch foo/foo/foo.txt
/tmp $ mkdir bar
/tmp $ cp --parents foo/foo/foo.txt bar
/tmp $ ls bar/foo/foo
foo.txt
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Why does += behave unexpectedly on lists?
...unction will append all elements of the parameter to the list.
When doing foo += something you're modifying the list foo in place, thus you don't change the reference that the name foo points to, but you're changing the list object directly. With foo = foo + something, you're actually creating a ne...
class
...
First, the class << foo syntax opens up foo's singleton class (eigenclass). This allows you to specialise the behaviour of methods called on that specific object.
a = 'foo'
class << a
def inspect
'"bar"'
end
end
a.inspect # =>...
SQL keys, MUL vs PRI vs UNI
...s example has neither PRI, MUL, nor UNI:
mysql> create table penguins (foo INT);
Query OK, 0 rows affected (0.01 sec)
mysql> desc penguins;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+...
Unsubscribe anonymous method in C#
... was to unsubscribe after the event was handled.
Example:
MyEventHandler foo = null;
foo = delegate(object s, MyEventArgs ev)
{
Console.WriteLine("I did it!");
MyEvent -= foo;
};
MyEvent += foo;
sh...
p vs puts in Ruby
...
p foo prints foo.inspect followed by a newline, i.e. it prints the value of inspect instead of to_s, which is more suitable for debugging (because you can e.g. tell the difference between 1, "1" and "2\b1", which you can't when...
Automatically expanding an R factor into a collection of 1/0 indicator variables for every factor le
...the ade4 package :
R> library(ade4)
R> df <-data.frame(eggs = c("foo", "foo", "bar", "bar"), ham = c("red","blue","green","red"))
R> acm.disjonctif(df)
eggs.bar eggs.foo ham.blue ham.green ham.red
1 0 1 0 0 1
2 0 1 1 0 ...
How to check if a variable is set in Bash?
...-------------+-----------------+-----------------+
| Expression | FOO="world" | FOO="" | unset FOO |
| in script: | (Set and Not Null) | (Set But Null) | (Unset) |
+--------------------+----------------------+-----------------+-----------------+
| $...
Regex: match everything but specific pattern
...t, but I think you could use a negative lookahead from the start, e.g. ^(?!foo).*$ shouldn't match anything starting with foo.
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How do you delete a column by name in data.table?
To get rid of a column named "foo" in a data.frame , I can do:
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