Skip to main content

Manipulating pandas data structures

I really enjoy using the Pandas Series and DataFrame objects. I find, however, that methods to update the series/frame are clunky. For a DataFrame it's pretty easy to add columns - you create a DataFrame or a Series and you just assign it. But adding rows to a Series or DataFrame is a bit clunky.

I sometimes have the need to modify a certain row with new data or add that row if it does not exist, which in a database would be a 'replace or insert' operation. You can concat or append another Series or DataFrame but I have not found a nice way of handling the 'replace or insert' case.

If the structure is small I simply convert it into a dictionary and manipulate the structure using the dictionary keys and then recreate the pandas structure.

If the structure is large I do an explicit test for the index (row) and then decide whether to append or replace.


Comments

Popular posts from this blog

A note on Python's __exit__() and errors

Python's context managers are a very neat way of handling code that needs a teardown once you are done. Python objects have do have a destructor method ( __del__ ) called right before the last instance of the object is about to be destroyed. You can do a teardown there. However there is a lot of fine print to the __del__ method. A cleaner way of doing tear-downs is through Python's context manager , manifested as the with keyword. class CrushMe: def __init__(self): self.f = open('test.txt', 'w') def foo(self, a, b): self.f.write(str(a - b)) def __enter__(self): return self def __exit__(self, exc_type, exc_val, exc_tb): self.f.close() return True with CrushMe() as c: c.foo(2, 3) One thing that is important, and that got me just now, is error handling. I made the mistake of ignoring all those 'junk' arguments ( exc_type, exc_val, exc_tb ). I just skimmed the docs and what popped out is that you need to return True or

Using adminer on Mac OS X

adminer is a nice php based sqlite manager. I prefer the firefox plugin "sqlite manager" but it currently has a strange issue with FF5 that basically makes it unworkable, so I was looking for an alternative to tide me over. I really don't want apache running all the time on my computer and don't want people browsing to my computer, so what I needed to do was: Download the adminer php script into /Library/WebServer/Documents/ Change /etc/apache2/httpd.conf to allow running of php scripts (uncomment the line that begins: LoadModule php5_module Start the apache server: sudo apachectl -k start Operate the script by going to localhost Stop the server: sudo apachectl -k stop