How to sort a Python DataFrame by second element of list

Question

So the title is a bit confusing but essentially, I have a Dataframe with two columns, one for the the character ("c") and one for the character's coordinates ("loc"). I would like to sort the dataframe by the Y coordinate. So far i have managed to sort the dataframe by the X cooridate using the sort_values() function:

df = pd.DataFrame({"c":["i", "a"," d","m"], "loc":[[1, 2], [3, 3], [4, 2], [3,5]]})
df.sort_values(by=["loc"], inplace=True)

which outputs:

    c   loc
0   i  [1, 2]
1   a  [3, 3]
3   m  [3, 5]
2   d  [4, 2]

The output I am aiming for is:

    c   loc
0   i  [1, 2]
2   d  [4, 2]
1   a  [3, 3]
3   m  [3, 5]

Cycling through the dataframe and inversing the y and x values is not an option as the full dataframe will be quite large. I do think this should be possible as the new version of pd.df.sort_values() has a "key" input (link to pd.df.sort_values() documentation), but I am not sufficiently familiar with the "key" input to properly execute this.

Scott Boston · Accepted Answer · 2021-08-12 17:41:31Z

3

Use key parameter in sort_values:

df.sort_values(by ='loc', key=lambda x: x.str[1])

Output:

    c     loc
0   i  [1, 2]
2   d  [4, 2]
1   a  [3, 3]
3   m  [3, 5]

answered Aug 12, 2021 at 17:41

Scott Boston

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3 Comments

anky Over a year ago

Quite similarly with argsort: df.iloc[df['loc'].str[1].argsort()]

benduvi20 Over a year ago

How would i then add for the second order of sorting is the X coordinate? ideally with Y in the descending order and X in ascending?

Scott Boston Over a year ago

@benduvi20 At this point I think you best separating X and Y in to columns in the dataframe then use sort_values with a list and a boolean list for ascending.

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