pandas ValueError: Length of values does not match length of index – Pandas DataFrame.unique() is an error which occurs when you try to assign a list/array in numpy to a data frame while both have different lengths.
In this article I am going to explain what happens when you get this error and how you can solve it with a main solution, we will also explore other solutions which can possibly solve the issue.
Exploring the pandas ValueError: Length of values does not match length of index – Pandas DataFrame.unique()
This is an error which occurs when you try to assign a list/array in numpy to a data frame while both have different lengths.
The error usually looks like the error bellow. Make sure yours is similar.
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ValueError: Length of values does not match length of index
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Bellow I make my best attempt at solving the error and present multiple possible solutions.
Solution : convert the array to a pandas Series using pd.Series( ).
The problem here is that we are trying to assign a list of numpy array to a data frame while they both have different lengths.
For example, if you take a dataframe of six rows , df = pd.DataFrame({‘X1’: [a,2,d,f,5,g]}) and assign a an array of five elements to it like in the code bellow. You will end up with the same error we have now.
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df['X2'] = [p,1,s,h]
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Now trying to assign a list/array of two elements to it:
The best solution to fix the problem is to convert the array to a pandas Series using pd.Series( ).
For the example above
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# instead of using
df['X2'] = [p,1,s,h]
# we can use the following pandas Series
df['X2'] = pd.Series([p,1,s,h])
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An other addition is to use reset_index( ) in order to reset the index.
Summing-up
This is the end of the article, the error could be confusing but with a little bit of investigating the error could be solved, thanks for reading our post and good luck with the scripts to come.
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