title: "unsupported operand type" error in numpy.corrcoef on pandas dataframe
body: <p>I have been trying to get correlation between dataframes with <code>numpy</code>, but I'm stuck with error:</p>
  <blockquote>
  <p>unsupported operand type(s) for +: 'float' and 'str'</p>
  </blockquote>
  <p>is there any wrong with my code, or what should I add? thank you</p>
  <pre><code>import pandas as pd
  
  usd = pd.read_csv(&quot;data_usd.csv&quot;)
  emas = pd.read_csv(&quot;emas_.csv&quot;)
  minyak = pd.read_csv(&quot;minyak_brent.csv&quot;)
  sawit = pd.read_csv(&quot;sawit.csv&quot;)
  kcl = pd.read_csv(&quot;kcl.csv&quot;)
  fosfat = pd.read_csv(&quot;fosfat.csv&quot;)
  
  
  df1 = pd.DataFrame(usd)
  df2 = pd.DataFrame(emas)
  df3 = pd.DataFrame(minyak)
  df4 = pd.DataFrame(sawit)
  df5 = pd.DataFrame(kcl)
  df6 = pd.DataFrame(fosfat)
  df_col = pd.concat([df1, df2, df3, df4, df5, df6], axis=1)
  df_col.columns
  df_col = df_col.set_index('month')
  df_col.head()
  import numpy as np
  np.corrcoef(df_col)
  </code></pre>