title: Need to sort a numpy array based on column value, but value is present in String format
body: <p>I am a newbie in python and need to extract info from a csv file containing terrorism data.</p>
  
  <p>I need to extract top 5 cities in India, having maximum casualities, where Casuality = Killed(given in CSV) + Wounded(given in CSV).
  City column is also given in the CSV file.</p>
  
  <p>Output format should be like below in descending order of casuality</p>
  
  <blockquote>
    <p>city_1 casualty_1  city_2 casualty_2  city_3 casualty_3  city_4
    casualty_4  city_5 casualty_5</p>
  </blockquote>
  
  <p>Link to CSV- <a href="https://ninjasdatascienceprod.s3.amazonaws.com/3571/terrorismData.csv?AWSAccessKeyId=AKIAIGEP3IQJKTNSRVMQ&amp;Expires=1554719430&amp;Signature=7uYCQ6pAb1xxPJhI%2FAfYeedUcdA%3D&amp;response-content-disposition=attachment%3B%20filename%3DterrorismData.csv" rel="nofollow noreferrer">https://ninjasdatascienceprod.s3.amazonaws.com/3571/terrorismData.csv?AWSAccessKeyId=AKIAIGEP3IQJKTNSRVMQ&amp;Expires=1554719430&amp;Signature=7uYCQ6pAb1xxPJhI%2FAfYeedUcdA%3D&amp;response-content-disposition=attachment%3B%20filename%3DterrorismData.csv</a></p>
  
  <pre><code>import numpy as np
  import csv
  file_obj=open("terrorismData.csv",encoding="utf8")
  file_data=csv.DictReader(file_obj,skipinitialspace=True)
  country=[]
  killed=[]
  wounded=[]
  city=[]
  final=[]
  
  #Making lists
  for row in file_data:
      if row['Country']=='India':
          country.append(row['Country'])
          killed.append(row['Killed'])
          wounded.append(row['Wounded'])
          city.append(row['City'])
          final.append([row['City'],row['Killed'],row['Wounded']])
  
  
  #Making numpy arrays out of lists
  np_month=np.array(country)
  np_killed=np.array(killed)
  np_wounded=np.array(wounded)
  np_city=np.array(city)
  np_final=np.array(final)
  
  
  #Fixing blank values in final arr
  for i in range(len(np_final)):
      for j in range(len(np_final[0])):
          if np_final[i][j]=='':
              np_final[i][j]='0.0'
  
  
  #Counting casualities(killed+wounded) and storing in 1st column of final array
  for i in range(len(np_final)):
      np_final[i,1]=float(np_final[i,1])+float(np_final[i,2])
  
  #Descending sort on casualities column
  np_final=np_final[np_final[:,1].argsort()[::-1]]
  </code></pre>
  
  <p>I expect np_final to get sorted on column casualities , but it's not happening because type(casualities) is coming as 'String'</p>
  
  <p>Any help is appreciated.</p>