Expected 2D array, got 1D array instead, Reshape Data

Question

I'm really stuck on this problem. I'm trying to use OneHotEncoder to encode my data into a matrix after using LabelEncoder but getting this error: Expected 2D array, got 1D array instead.

At the end of the error message(included below) it said to "Reshape my data" which I thought I did but it's still not working. If I understand Reshaping, is that just when you want to literally reshape some data into a different matrix size? For example, if I want to change a 3 x 2 matrix into a 4 x 6?

My code is failing on these 2 lines:

X = X.reshape(-1, 1) # I added this after I saw the error
X[:, 0] = onehotencoder1.fit_transform(X[:, 0]).toarray()

Here is the code I have so far:

# Data Preprocessing

# Import Libraries
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd

# Import Dataset
dataset = pd.read_csv('Data2.csv')
X = dataset.iloc[:, :-1].values
y = dataset.iloc[:, 5].values
df_X = pd.DataFrame(X)
df_y = pd.DataFrame(y)

# Replace Missing Values
from sklearn.preprocessing import Imputer
imputer = Imputer(missing_values = 'NaN', strategy = 'mean', axis = 0)
imputer = imputer.fit(X[:, 3:5 ])
X[:, 3:5] = imputer.transform(X[:, 3:5])


# Encoding Categorical Data "Name"
from sklearn.preprocessing import LabelEncoder, OneHotEncoder
labelencoder_x = LabelEncoder()
X[:, 0] = labelencoder_x.fit_transform(X[:, 0])

# Transform into a Matrix

onehotencoder1 = OneHotEncoder(categorical_features = [0])
X = X.reshape(-1, 1)
X[:, 0] = onehotencoder1.fit_transform(X[:, 0]).toarray()


# Encoding Categorical Data "University"
from sklearn.preprocessing import LabelEncoder
labelencoder_x1 = LabelEncoder()
X[:, 1] = labelencoder_x1.fit_transform(X[:, 1])

Here is the full error message:

 File "/Users/jim/anaconda3/lib/python3.6/site-packages/sklearn/preprocessing/data.py", line 1809, in _transform_selected
    X = check_array(X, accept_sparse='csc', copy=copy, dtype=FLOAT_DTYPES)

  File "/Users/jim/anaconda3/lib/python3.6/site-packages/sklearn/utils/validation.py", line 441, in check_array
    "if it contains a single sample.".format(array))

ValueError: Expected 2D array, got 1D array instead:
array=[  2.00000000e+00   7.00000000e+00   3.20000000e+00   2.70000000e+01
   2.30000000e+03   1.00000000e+00   6.00000000e+00   3.90000000e+00
   2.80000000e+01   2.90000000e+03   3.00000000e+00   4.00000000e+00
   4.00000000e+00   3.00000000e+01   2.76700000e+03   2.00000000e+00
   8.00000000e+00   3.20000000e+00   2.70000000e+01   2.30000000e+03
   3.00000000e+00   0.00000000e+00   4.00000000e+00   3.00000000e+01
   2.48522222e+03   5.00000000e+00   9.00000000e+00   3.50000000e+00
   2.50000000e+01   2.50000000e+03   5.00000000e+00   1.00000000e+00
   3.50000000e+00   2.50000000e+01   2.50000000e+03   0.00000000e+00
   2.00000000e+00   3.00000000e+00   2.90000000e+01   2.40000000e+03
   4.00000000e+00   3.00000000e+00   3.70000000e+00   2.77777778e+01
   2.30000000e+03   0.00000000e+00   5.00000000e+00   3.00000000e+00
   2.90000000e+01   2.40000000e+03].
Reshape your data either using array.reshape(-1, 1) if your data has a single feature or array.reshape(1, -1) if it contains a single sample.

Any help would be great.

Answer 1

Ok I finally got the code to work. Please see the solution below:

# Data Preprocessing

# Import Libraries
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd

# Import Dataset
dataset = pd.read_csv('Data2.csv')
X = dataset.iloc[:, :-1].values
y = dataset.iloc[:, 5].values
df_X = pd.DataFrame(X)
df_y = pd.DataFrame(y)

# Replace Missing Values
from sklearn.preprocessing import Imputer
imputer = Imputer(missing_values = 'NaN', strategy = 'mean', axis = 0)
imputer = imputer.fit(X[:, 3:5 ])
X[:, 3:5] = imputer.transform(X[:, 3:5])


# Encoding Categorical Data "Name"
from sklearn.preprocessing import LabelEncoder, OneHotEncoder
labelencoder_x = LabelEncoder()
X[:, 0] = labelencoder_x.fit_transform(X[:, 0])


# Encoding Categorical Data "University"
from sklearn.preprocessing import LabelEncoder
labelencoder_x1 = LabelEncoder()
X[:, 1] = labelencoder_x1.fit_transform(X[:, 1])


# Transform Name into a Matrix
onehotencoder1 = OneHotEncoder(categorical_features = [0])
X = onehotencoder1.fit_transform(X).toarray()

# Transform University into a Matrix
onehotencoder2 = OneHotEncoder(categorical_features = [6])
X = onehotencoder2.fit_transform(X).toarray()