"Series objects are mutable and cannot be hashed" error

Question

I am trying to get the following script to work. The input file consists of 3 columns: gene association type, gene name, and disease name.

cols = ['Gene type', 'Gene name', 'Disorder name'] no_headers = pd.read_csv('orphanet_infoneeded.csv', sep=',',header=None,names=cols)  gene_type = no_headers.iloc[1:,[0]] gene_name = no_headers.iloc[1:,[1]] disease_name = no_headers.iloc[1:,[2]]  query = 'Disease-causing germline mutation(s) in' ###add query as required  orph_dict = {}  for x in gene_name:     if gene_name[x] in orph_dict:         if gene_type[x] == query:             orph_dict[gene_name[x]]=+ 1         else:             pass     else:         orph_dict[gene_name[x]] = 0 

I keep getting an error that says:

Series objects are mutable and cannot be hashed

Any help would be dearly appreciated!

Answer 1

Shortly: gene_name[x] is a mutable object so it cannot be hashed. To use an object as a key in a dictionary, python needs to use its hash value, and that's why you get an error.

Further explanation:

Mutable objects are objects which value can be changed. For example, list is a mutable object, since you can append to it. int is an immutable object, because you can't change it. When you do:

a = 5; a = 3; 

You don't change the value of a, you create a new object and make a point to its value.

Mutable objects cannot be hashed. See this answer.

To solve your problem, you should use immutable objects as keys in your dictionary. For example: tuple, string, int.