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.

Your array is 1D it has to be 2D .... where ever you are getting the error just add `numpy.asmatrix(data)` where data is the data that you are passing... or you can reshape ... Passing 1D array has been deprecated in recent versions of sklearn — Jai, Dec 25 '17 at 02:12
Hi @JayShah in my code I added: X = X.reshape(-1, 1). Is this the correct way to reshape data? — wolfbagel, Dec 25 '17 at 02:15
yes `X = X.reshape(-1, 1)` is the right way is to reshape data but in the error but this will only work if your X is a **numpy array** and not **list**... If it is a list than make your array list of list ... from the error message I can clearly see `array = [ ]` is 1D because it has one opening and clasing brackets and after reshaping please remove `X[:, 1]` in transform and just put X — Jai, Dec 25 '17 at 02:25

Jai · Answer 1 · 2017-12-25T02:37:08.740

try changing you code to this

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])
res_0 = onehotencoder1.fit_transform(X[:, 0].reshape(-1, 1))  # <=== Change
X[:, 0] = res_0.ravel()

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

If you are getting error at labelencoder_x1.fit_transform(X[:, 1]) then make it labelencoder_x1.fit_transform(X[:, 1].reshape(-1, 1))

Thanks for the solution! I'm running it line by line but it's failing on this line: "X[:, 0] = res_0.ravel()", saying "ravel not found". — wolfbagel, Dec 25 '17 at 02:51

score 0 · Accepted Answer · answered Dec 25 '17 at 03:18

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()

score 0 · Answer 3 · answered Nov 19 '19 at 16:05

I got same error when I was trying to do same. I was transforming single column of data. Here, how I override this problem

encoding_X = OneHotEncoder(categories = [np.unique(X[:,0]).tolist()])
encoding_X.fit(np.unique(X[:,0]).reshape(-1,1).tolist())
encoding_X.transform(X[:,0].reshape(-1,1).tolist()).toarray()

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

3 Answers3