Expected 2D array, got 1D array instead: after fitting the model

Question

I don't understand where i'm getting wrong. Both of the arrays are of same shape and has same no. of elements. i'm getting - "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."

I'll provide my code below -

y_pred:
    array([1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1,
           1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1,
           0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1,
           0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 1,
           0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1,
           1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0,
           1, 1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1,
           1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 1, 0,
           1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
           0, 1], dtype=int64)
   

 y_pred.shape - (200,)
    
   
 y_test :array([1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1,
           1, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1,
           0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1,
           0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0,
           0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1,
           1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0,
           0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1,
           1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0,
           1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
           0, 1], dtype=int64)
    

y_test.shape -  (200,)

Now when i tried to evaluate this (dtc.score(y_test,y_pred_dtr)) , I'm getting this error -

ValueError: Expected 2D array, got 1D array instead:
    array=[1. 0. 0. 0. 0. 0. 1. 0. 0. 1. 1. 1. 0. 0. 1. 0. 1. 0. 0. 1. 1. 1. 1. 1.
     0. 1. 0. 0. 0. 1. 0. 1. 1. 0. 0. 0. 0. 0. 0. 0. 0. 1. 0. 1. 0. 0. 0. 1.
     1. 0. 1. 1. 1. 0. 1. 0. 1. 0. 0. 0. 1. 1. 1. 0. 1. 1. 0. 1. 0. 1. 1. 0.
     0. 0. 0. 1. 1. 1. 1. 1. 0. 0. 1. 1. 1. 0. 1. 0. 0. 0. 1. 0. 0. 1. 1. 0.
     0. 0. 0. 1. 0. 0. 1. 0. 0. 1. 1. 0. 0. 1. 1. 1. 1. 1. 1. 0. 0. 0. 0. 1.
     1. 1. 0. 0. 0. 1. 0. 1. 1. 1. 0. 0. 0. 1. 1. 0. 1. 1. 1. 0. 0. 0. 1. 1.
     0. 1. 0. 0. 0. 0. 1. 0. 0. 1. 1. 0. 0. 0. 0. 1. 1. 0. 1. 0. 1. 0. 1. 1.
     0. 0. 1. 0. 1. 1. 1. 0. 1. 1. 1. 1. 0. 1. 0. 1. 1. 1. 1. 0. 1. 0. 0. 0.
     0. 0. 0. 0. 0. 0. 0. 1.].
    

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.

When your are doing dtc.score(y_test, y_pred_dtr). When did you obtained y_pred_dtr? I only see y_pred. Also, I can see that you don't obtain a normal array, values are no separated by commas. I don't know if its an error of copying the output — Alex Serra Marrugat
– Alex Serra Marrugat, Commented Jan 11, 2021 at 8:15
@AlexSerraMarrugat I did : y_pred = dtc.predict(x_test). this is how i got value of y_pred. — user14981754
– user14981754, Commented Jan 11, 2021 at 8:22
Yes, but in your score you write: y_pred_dtr. This a variable you haven't defined yet. Can you check it? — Alex Serra Marrugat
– Alex Serra Marrugat, Commented Jan 11, 2021 at 8:28
@AlexSerraMarrugat i wrote that by mistake in the comment , i calculated the y_pred_dtr — user14981754
– user14981754, Commented Jan 11, 2021 at 12:11

Abrar Malekji · Accepted Answer · 2021-01-11 09:32:46Z

1

here is the thing,
a=np.array([1,2,3]) is 1D array
now in y_pred and y_test it should be 
array=np.array([sample1array,sample2array,....])
so it should be,
a=np.array([[1],[2],[3]])
so try reshape(-1,1) so
np.array([1,2,3]) will be converted 'n' rows '1' column array (2D) = np.array([[1],[2],[3]]).
try this.

EDIT: because it may be possible that your output length is greater than 1 then? ,like y=[[1,0],[0,0],[1,0]]. this is the only way to do that. thanks.

edited Jan 11, 2021 at 9:32

answered Jan 11, 2021 at 8:18

Abrar Malekji

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2 Comments

user14981754 Over a year ago

I understood that but i have to reshape both the arrays ? also why do we need 2D arrays for evaluating the score of model ?

user14981754 Over a year ago

sorry but no, both the array are of same shape , i have mentioned that in the question . Both the arrays are 1D and have 200 values in it.

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