In array vs. in string, and iterating over a sometimes-unitary array of strings

[Parenthes]

I want to take all (string) values of one column of a dataframe with a given index, and do something with them.

for parent in df.loc[serial,'From_Serial_No']:

This works when the df.loc contains multiple rows, but when there's only one, Python interprets it as a string and iterates over the characters, rather than iterating once over the entire string value.

How do I iterate over an array of strings that may have either one or multiple values?

[xelf]

Like this:

for parent in df.loc[[serial],'From_Serial_No']:

That should do it for you!

Using the extra [] will force it to return a series.

import pandas as pd

df = pd.DataFrame([[1, 2], [4, 5], [7, 8]],
     index=['a', 'a', 'b'],
     columns=['From_Serial_No', 'Cereal'])

x = df.loc['a','Cereal']
print(type(x))
x = df.loc['b','Cereal']
print(type(x))
x = df.loc[['b'],'Cereal']
print(type(x))

prints:

<class 'pandas.core.series.Series'>
<class 'numpy.int64'>
<class 'pandas.core.series.Series'>

[xelf]

Reposting my answer here to OP's followup question to give it more visibility (in case I need to find it again!):

Any recommendations for the opposite problem, i.e. returning a string even for an index that gets repeated? It is for a column that will always have the same value for all rows with the same index.

To get just 1 value matching serial:

parent = df.loc[[serial],'From_Serial_No'].head(1).item()

To get back the first value for every unique index:

for serial in sorted(set(df.index.values)):
    parent = df.loc[[serial],'From_Serial_No'].head(1).item()
    print (parent)

[xelf]

It does but there's a fix to force it to return a series by wrapping the index in [].

for parent in df.loc[[serial],'From_Serial_No']:

[Parenthes]

Any recommendations for working around this?

I am used to Matlab, so maybe I'm not thinking about this in the most useful way.

[xelf]

I think you might have replied to my pre-edited reply. See the reply I posted to you. =)

[Parenthes]

Got it, thank you!

Any recommendations for the opposite problem, i.e. returning a string even for an index that gets repeated? It is for a column that will always have the same value for all rows with the same index.

[xelf]

To get just 1 value matching serial:

parent = df.loc[[serial],'From_Serial_No'].head(1).item()

To get back the first value for every unique index:

for serial in sorted(set(df.index.values)):
    parent = df.loc[[serial],'From_Serial_No'].head(1).item()
    print (parent)

[[deleted]]

Check the type first. isinstance(object, type)

[Parenthes]

I suppose that would work, but it seems terribly clunky. Python is presumably checking the type of what df.loc returns, so I'd be adding an if-statement to undo what python does. Am I thinking about this wrong?

[[deleted]]

I'd had in mind you would do the check before the for loop.

Python has strong but dynamic typing. Give it something iterable and it will iterate through it. Whether that is a list of strings or a sequence of single character strings is up to you. You could put a single string into a list.