title: cannot concatenate object of type "<class 'numpy.ndarray'>"; only pd.Series, pd.DataFrame, and pd.Panel (deprecated) objs are valid
body: <p>My input data is under the form:</p>
  <pre><code>    gold,Program,MethodType,CallersT,CallersN,CallersU,CallersCallersT,CallersCallersN,CallersCallersU,CalleesT,CalleesN,CalleesU,CalleesCalleesT,CalleesCalleesN,CalleesCalleesU,CompleteCallersCallees,classGold
  T,chess,Inner,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,-1,Low,1,Trace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,Low,1,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,Low,1,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,Low,1,Trace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,Low,1,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,Low,1,Trace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,Low,1,Trace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,High,-1,-1,-1,Low,1,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,Medium,Medium,-1,High,High,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,Medium,Medium,-1,High,High,0,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,Medium,Medium,-1,High,High,0,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,Medium,Medium,-1,High,High,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,Medium,Medium,-1,High,High,0,NoTrace,
  T,chess,Inner,Low,-1,-1,Low,-1,-1,Medium,-1,Medium,High,-1,High,0,Trace,
  T,chess,Inner,Low,-1,-1,Low,-1,-1,Medium,-1,Medium,High,-1,High,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,Low,-1,-1,Medium,Medium,-1,High,High,0,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,-1,-1,Low,Low,High,Medium,-1,Medium,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,-1,-1,-1,Medium,High,Low,Low,Medium,0,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,-1,-1,-1,Medium,High,-1,Medium,Medium,0,NoTrace,
  T,chess,Inner,-1,Low,-1,-1,-1,-1,-1,Medium,High,Low,Low,Medium,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,-1,-1,-1,Medium,High,-1,Medium,Medium,0,NoTrace,
  N,chess,Inner,-1,Low,-1,-1,-1,-1,Low,Low,High,Low,Low,Medium,0,Trace,
  N,chess,Inner,Low,-1,-1,-1,-1,-1,Low,Low,High,Low,Low,Medium,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,-1,-1,-1,Medium,High,-1,Medium,Medium,0,NoTrace,
  ....
  N,chess,Inner,-1,Low,-1,-1,Medium,-1,-1,Low,Low,-1,-1,-1,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,Medium,-1,-1,Low,Low,-1,-1,-1,0,NoTrace,
  T,chess,Inner,Low,-1,-1,Low,Low,-1,Low,-1,Low,-1,-1,-1,0,Trace,
  T,chess,Inner,Low,-1,-1,Medium,-1,-1,Low,-1,Low,-1,-1,-1,0,Trace,
  N,chess,Inner,-1,Low,-1,-1,Medium,-1,-1,Low,Low,-1,-1,-1,0,NoTrace,
  </code></pre>
  <p>I am reading my data and I am trying to concatenate two data sets that are subsets of the original data set, here is the code I am using:</p>
  <pre><code>    import pandas as pd
  import numpy as np
  from sklearn.feature_selection import SelectFromModel
  from sklearn.model_selection import train_test_split
  # Feature Scaling
  from sklearn.preprocessing import StandardScaler
  SeparateProjectLearning=False
  CompleteCallersCallees=False
  PartialTrainingSetCompleteCallersCallees=True
  def main():
      X_train={}
      X_test={}
      y_train={}
      y_test={}
      dataset = pd.read_csv( 'InputData.txt', sep= ',', index_col=False) 
      #convert T into 1 and N into 0
      dataset['gold'] = dataset['gold'].astype('category').cat.codes
      dataset['Program'] = dataset['Program'].astype('category').cat.codes
      dataset['classGold'] = dataset['classGold'].astype('category').cat.codes
      dataset['MethodType'] = dataset['MethodType'].astype('category').cat.codes
      
      dataset['CallersT'] = dataset['CallersT'].astype('category').cat.codes
      dataset['CallersN'] = dataset['CallersN'].astype('category').cat.codes
      dataset['CallersU'] = dataset['CallersU'].astype('category').cat.codes
      dataset['CallersCallersT'] = dataset['CallersCallersT'].astype('category').cat.codes
      dataset['CallersCallersN'] = dataset['CallersCallersN'].astype('category').cat.codes
      dataset['CallersCallersU'] = dataset['CallersCallersU'].astype('category').cat.codes
      dataset['CalleesT'] = dataset['CalleesT'].astype('category').cat.codes
      dataset['CalleesN'] = dataset['CalleesN'].astype('category').cat.codes
      dataset['CalleesU'] = dataset['CalleesU'].astype('category').cat.codes
      dataset['CalleesCalleesT'] = dataset['CalleesCalleesT'].astype('category').cat.codes
      dataset['CalleesCalleesN'] = dataset['CalleesCalleesN'].astype('category').cat.codes
      dataset['CalleesCalleesU'] = dataset['CalleesCalleesU'].astype('category').cat.codes 
      pd.set_option('display.max_columns', None)
      row_count, column_count = dataset.shape
      Xcol = dataset.iloc[:, 1:column_count]
          
                
      
      
      CompleteSet=dataset.loc[dataset['CompleteCallersCallees'] == 1]
      CompleteSet_X = CompleteSet.iloc[:, 1:column_count].values
      CompleteSet_Y = CompleteSet.iloc[:, 0].values
      X_train, X_test, y_train, y_test = train_test_split(CompleteSet_X, CompleteSet_Y, test_size = 0.2, random_state = 0)
      TestSet=dataset.loc[dataset['CompleteCallersCallees'] == 0]
      X_test1=TestSet.iloc[:, 1:column_count].values
      X_test=pd.concat(X_test1,X_test)
  </code></pre>
  <p>I want to build my own test set and training set by using concatenation and I am trying to concatenate <code>X_test1</code> and <code>X_test</code> in the code above. However, the problem is that I am getting an error for the last line of code  <code>X_test=pd.concat(X_test1,X_test)</code> and the error says <code>TypeError: cannot concatenate object of type &quot;&lt;class 'numpy.ndarray'&gt;&quot;; only pd.Series, pd.DataFrame, and pd.Panel (deprecated) objs are valid</code>. How can I fix this?</p>