docstr: Evaluate the retrieval model
docstr_tok: ["Evaluate","the","retrieval","model"]
code: def evaluate_retrieval(self):
      """Evaluate the retrieval model"""
  
      df = self.df.copy(deep=True)
  
      # get question answering results
      df["retrieved_context"] = df.apply(
          lambda x: self.extract_returned_text(
              self.query_vector_store(x["question"])
          ),
          axis=1,
      )
  
      # embed context and retrieved context
      context_embeddings = self.embed_texts(df["context"].tolist())
      retrieved_context_embeddings = self.embed_texts(
          df["retrieved_context"].tolist()
      )
  
      df = self.calculate_retrieval_metrics(
          df, context_embeddings, retrieved_context_embeddings
      )
  
      return df
  
imports: import ast
  from collections import defaultdict
  from typing import List
  import nltk
  import pandas
  from nltk import word_tokenize
  from nltk.translate.bleu_score import sentence_bleu
  from nltk.translate.meteor_score import meteor_score
  from rouge_score import rouge_scorer
  from scipy.spatial import distance
  from mindsdb.integrations.handlers.writer_handler.settings import WriterHandlerParameters
  from mindsdb.utilities import log
label_desc: Use image node_id 21 for calling the WriterEvaluator obj's underlying member method code with example usage: obj.evaluate_retrieval() and returns: df