try loc a column with list pandas - index not found

Question

I have a fixed array eg sort_by = [a,b,c,d,e,f] . My dataframe looks like this, I have made Column1 my index:

Column1 | Column2 | ...
   d         1         
   d         2
   b         3
   a         4
   a         5
   b         6
   c         7

I want to loc from the sort_by list to sort them, however, sometimes not all values of sort_by are in Column which results in index not found. How do I get it to "try" to the best of its ability?

s.set_index('mitre_attack_tactic', inplace=True)
print(s.loc[sort_by]) --> doesn't work
print(s.loc[[a,b,c,d]) --> does work however Column1 could have e,f,g

Answer 1

You can use the key of df.sort_values . Idea is to create a value index dictionary from sort_by list then map the dictionary to column and sort by the resulted index.

key = {v:k for k, v in enumerate(sort_by)}
df = df.sort_values('Column1', key=lambda col: col.map(key))

print(df)

  Column1  Column2
3       a        4
4       a        5
2       b        3
5       b        6
6       c        7
0       d        1
1       d        2

Answer 2

Let us try pd.Categorical

out = df.iloc[pd.Categorical(df.Column1,['a','b','c','d']).argsort()]
Out[48]: 
  Column1  Column2
3       a        4
4       a        5
2       b        3
5       b        6
6       c        7
0       d        1
1       d        2

Answer 3

This page helps:

If you create your sort_by as a categorical:

sort_by = pd.api.types.CategoricalDtype(["a","b","c","d","e","f"], ordered=True)

Then change your column to a categorical:

s['Column1'] = s['Column1'].astype(sort_by)

You can then sort it:

s.sort_values('Column1')

Answer 4

index.intersection

df.loc[pd.Index(sort_by).intersection(df.index)]

---

   Column2
a        4
a        5
b        3
b        6
c        7
d        1
d        2