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How to create a MySQL hierarchical recursive query
...) initialisation
where find_in_set(parent_id, @pv)
and length(@pv := concat(@pv, ',', id))
Here is a fiddle.
Here, the value specified in @pv := '19' should be set to the id of the parent you want to select all the descendants of.
This will work also if a parent has multiple children. Howe...
Is there any haskell function to concatenate list with separator?
Is there a function to concatenate elements of a list with a separator?
For example:
5 Answers
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Can I “multiply” a string (in C#)?
...
In .NET 4 you can do this:
String.Concat(Enumerable.Repeat("Hello", 4))
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JavaScript variable number of arguments to function
...rty. This includes the arguments object. Knowing this, and that the method concat returns a copy of the 'array' it's called on, we can easily convert the arguments object to a real array like this: var args = [].concat.call(arguments). Some people prefer to use Array.prototype.concat.call instead, b...
How to combine paths in Java?
...oes have a class FilenameUtils that can do this kind of thing, such as the concat() method.
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Pandas groupby: How to get a union of strings
...is!
3 3 0.463468 a
4 4 0.643961 random
sum by default concatenates
In [9]: df.groupby('A')['C'].apply(lambda x: x.sum())
Out[9]:
A
1 Thisstring
2 is!
3 a
4 random
dtype: object
You can do pretty much what you want
In [11]: df.groupby('A')['C'...
Transposing a 2D-array in JavaScript
...rix.reduce((prev, next) => next.map((item, i) =>
(prev[i] || []).concat(next[i])
), []);
}
Lodash/Underscore by marcel
function tranpose(matrix) {
return _.zip(...matrix);
}
// Without spread operator.
function transpose(matrix) {
return _.zip.apply(_, [[1,2,3], [1,2,3], [1,2,3]]...
How to import data from mongodb to pandas?
...64"] arrays = client.query("db_tmp", "coll", {}, columns, data_type) For 50000 records takes around 200s.
– nishant
Nov 27 '17 at 11:09
...
Creating an empty Pandas DataFrame, then filling it?
...ire handling the index appropriately).
Things you should NOT do
append or concat inside a loop
Here is the biggest mistake I've seen from beginners:
df = pd.DataFrame(columns=['A', 'B', 'C'])
for a, b, c in some_function_that_yields_data():
df = df.append({'A': i, 'B': b, 'C': c}, ignore_index=...
How do I create a PDO parameterized query with a LIKE statement?
...e LIKE with % partial matching for MySQL databases: WHERE column_name LIKE CONCAT('%', :dangerousstring, '%')
where the named parameter is :dangerousstring.
In other words, use explicitly unescaped % signs in your own query that are separated and definitely not the user input.
Edit: Concatenati...