title: ValueError: array length does not match index length
body: <p>I am practicing for contests like kaggle and I have been trying to use XGBoost and am trying to get myself familiar with python 3rd party libraries like pandas and numpy.</p>
  
  <p>I have been reviewing scripts from this particular competition called the Santander Customer Satisfaction Classification and I have been modifying different forked scripts in order to experiment on them.</p>
  
  <p>Here is one modified script through which I am trying to implement XGBoost:</p>
  
  <pre><code>import pandas as pd
  from sklearn import cross_validation as cv
  import xgboost as xgb
  
  df_train = pd.read_csv("/Users/pavan7vasan/Desktop/Machine_Learning/Project Datasets/Santander_Customer_Satisfaction/train.csv")
  df_test  = pd.read_csv("/Users/pavan7vasan/Desktop/Machine_Learning/Project Datasets/Santander_Customer_Satisfaction/test.csv")   
  
  df_train = df_train.replace(-999999,2)
  
  id_test = df_test['ID']
  y_train = df_train['TARGET'].values
  X_train = df_train.drop(['ID','TARGET'], axis=1).values
  X_test = df_test.drop(['ID'], axis=1).values
  
  X_train, X_test, y_train, y_test = cv.train_test_split(X_train, y_train, random_state=1301, test_size=0.4)
  
  clf = xgb.XGBClassifier(objective='binary:logistic',
                  missing=9999999999,
                  max_depth = 7,
                  n_estimators=200,
                  learning_rate=0.1, 
                  nthread=4,
                  subsample=1.0,
                  colsample_bytree=0.5,
                  min_child_weight = 3,
                  reg_alpha=0.01,
                  seed=7)
  
  clf.fit(X_train, y_train, early_stopping_rounds=50, eval_metric="auc", eval_set=[(X_train, y_train), (X_test, y_test)])
  y_pred = clf.predict_proba(X_test)
  
  print("Cross validating and checking the score...")
  scores = cv.cross_val_score(clf, X_train, y_train) 
  '''
  test = []
  result = []
  for each in id_test:
      test.append(each)
  for each in y_pred[:,1]:
      result.append(each)
  
  print len(test)
  print len(result)
  '''
  submission = pd.DataFrame({"ID":id_test, "TARGET":y_pred[:,1]})
  #submission = pd.DataFrame({"ID":test, "TARGET":result})
  submission.to_csv("submission_XGB_Pavan.csv", index=False)
  </code></pre>
  
  <p>Here is the stacktrace :</p>
  
  <pre><code>Traceback (most recent call last):
    File "/Users/pavan7vasan/Documents/workspace/Machine_Learning_Project/Kaggle/XG_Boost.py", line 45, in &lt;module&gt;
  submission = pd.DataFrame({"ID":id_test, "TARGET":y_pred[:,1]})
    File "/anaconda/lib/python2.7/site-packages/pandas/core/frame.py", line 214, in __init__
  mgr = self._init_dict(data, index, columns, dtype=dtype)
    File "/anaconda/lib/python2.7/site-packages/pandas/core/frame.py", line 341, in _init_dict
  dtype=dtype)
    File "/anaconda/lib/python2.7/site-packages/pandas/core/frame.py", line 4798, in _arrays_to_mgr
  index = extract_index(arrays)
    File "/anaconda/lib/python2.7/site-packages/pandas/core/frame.py", line 4856, in extract_index
  raise ValueError(msg)
  ValueError: array length 30408 does not match index length 75818
  </code></pre>
  
  <p>I have tried solutions based on my searches for different solutions, but I am not able to figure out what the mistake is. What is it that I have gone wrong in? Please let me know</p>