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pandas three-way joining multiple dataframes on columns
...dataframes). It's worth noting that if your join keys are unique, using pd.concat will result in simpler syntax: pd.concat([df.set_index('name') for df in dfs], axis=1, join='inner').reset_index(). concat is also more versatile when dealing with duplicate column names across multiple dfs (join isn't...
Immutability of Strings in Java
...y its method. It will create all new String object in pool as follows.
s1.concat(" overflow");
___________________
| |
s1.concat ----> | stack overflow |
|___________________|
out.println(s1); // o/p: stack
out.println(s2...
MySQL - Rows to Columns
...you need to pivot is to let mysql build the query for you:
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'ifnull(SUM(case when itemname = ''',
itemname,
''' then itemvalue end),0) AS `',
itemname, '`'
)
) INTO @sql
FROM
history;
SET @sql = CONCAT('SELECT hostid, ', @sql...
Duplicating a MySQL table, indices, and data
...char(255))
BEGIN
-- DROP TABLE IF EXISTS GLS_DEVICES_OLD;
SET @query = concat('DROP TABLE IF EXISTS ',tbl_name,'_OLD');
PREPARE stmt FROM @query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
-- CREATE TABLE GLS_DEVICES_NEW LIKE GLS_DEVICES;
SET @query = concat('CREATE TABLE ',tbl_name,'_NEW...
How do I convert from BLOB to TEXT in MySQL?
...
This works great for those GROUP_CONCATs that convert your output to blobs and you really want them as strings. I had an issue similar to the OP's while using Node.JS with the node-mysql library - this fixed all group_concat issues.
– m...
Create an array with same element repeated multiple times
...== 0) return [];
var a = [value];
while (a.length * 2 <= len) a = a.concat(a);
if (a.length < len) a = a.concat(a.slice(0, len - a.length));
return a;
}
It doubles the array in each iteration, so it can create a really large array with few iterations.
Note: You can also improve yo...
For loop example in MySQL
... declare x INT default 0;
SET x = 1;
WHILE x <= 5 DO
SET str = CONCAT(str,x,',');
SET x = x + 1;
END WHILE;
select str;
END//
Which prints:
mysql> call while_example();
+------------+
| str |
+------------+
| 1,2,3,4,5, |
+------------+
REPEAT loop syntax example ...
Add to Array jQuery
...
For JavaScript arrays, you use Both push() and concat() function.
var array = [1, 2, 3];
array.push(4, 5); //use push for appending a single array.
var array1 = [1, 2, 3];
var array2 = [4, 5, 6];
var array3 = array1.concat(array2); //It is better use conca...
Prepend a level to a pandas MultiIndex
...
A nice way to do this in one line using pandas.concat():
import pandas as pd
pd.concat([df], keys=['Foo'], names=['Firstlevel'])
An even shorter way:
pd.concat({'Foo': df}, names=['Firstlevel'])
This can be generalized to many data frames, see the docs.
...
Easy way to concatenate two byte arrays
What is the easy way to concatenate two byte arrays?
12 Answers
12
...