Sort a list of numerical strings in ascending order

Question

I have created a sqlite database which has a table which stores temperature values  The temperature values are written to the database in ascending order for the first time  Then I read the temperature values from the database into a list and then add that list to a combo box to select temperatures - works fine    The resulting list is  say   templist     25    50    100    150    200    250    300      Then I add a new temperature value  say   33  to the database    It gets appended to the end of the table  If I read the temperatures now  the list will become      25    50    100    150    200    250    300    33       If I do templist sort   or sorted templist   the end result is     150    200    25    250    300    33    50     Is there any simple way to sort the list in ascending order so that I get     25    33    50    100    150    200    250    300

User · Accepted Answer

The recommended approach in this case is to sort the data in the database, adding an ORDER BY at the end of the query that fetches the results, something like this:

SELECT temperature FROM temperatures ORDER BY temperature ASC;  -- ascending order
SELECT temperature FROM temperatures ORDER BY temperature DESC; -- descending order

If for some reason that is not an option, you can change the sorting order like this in Python:

templist = [25, 50, 100, 150, 200, 250, 300, 33]
sorted(templist, key=int)               # ascending order
> [25, 33, 50, 100, 150, 200, 250, 300]
sorted(templist, key=int, reverse=True) # descending order
> [300, 250, 200, 150, 100, 50, 33, 25]

As has been pointed in the comments, the int key (or float if values with decimals are being stored) is required for correctly sorting the data if the data received is of type string, but it'd be very strange to store temperature values as strings, if that is the case, go back and fix the problem at the root, and make sure that the temperatures being stored are numbers.

User · Answer

in python sorted works like you want with integers    gt  gt  gt  sorted  10 3 2    2  3  10    it looks like you have a problem because you are using strings    gt  gt  gt  sorted   10   3   2      10    2    3      because string ordering starts with the first character  and  1  comes before  2   no matter what characters follow  which can be fixed with key int   gt  gt  gt  sorted   10   3   2    key int    2    3    10     which converts the values to integers during the sort  it is called as a function - int  10   returns the integer 10   and as suggested in the comments  you can also sort the list itself  rather than generating a new one    gt  gt  gt  l     10   3   2    gt  gt  gt  l sort key int   gt  gt  gt  l   2    3    10     but i would look into why you have strings at all   you should be able to save and retrieve integers   it looks like you are saving a string when you should be saving an int    sqlite is unusual amongst databases  in that it kind-of stores data in the same type as it is given  even if the table column type is different    and once you start saving integers  you can also get the list back sorted from sqlite by adding order by     to the sql command   select temperature from temperatures order by temperature

[python] Sort a list of numerical strings in ascending order

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