GridSearchCV is Giving me ValueError: number of labels does not match number of samples

Question

I'm trying to run a grid CV parameter search using sklearn.model_selection.GridSearchCV. I keep getting a ValueError that is really confusing me. Below I've included the code for the pipeline I created, which includes a TfidfVectorizer and a RandomForestClassifier. I used train_test_split to separate the features and target, and tried to fit the grid search with the pipeline. Here are my results.

from sklearn.model_selection import train_test_split, GridSearchCV
from sklearn.pipeline import Pipeline
from sklearn.ensemble import RandomForestClassifier
from sklearn.feature_extraction.text import TfidfVectorizer

features = ['id', 'description']
target = 'ratingCategory'
x_train, x_val, y_train, y_val = train_test_split(
    train[features],
    train[target],
    test_size=0.2,
    stratify=train[target],
    random_state=95
)

vect = TfidfVectorizer()
clf = RandomForestClassifier()

pipe = Pipeline([
    ('vect', vect), 
    ('clf', clf)]
)

parameters = {
    'vect__min_df': (0.01, 0.05),
    'clf__ccp_alpha': (0.1, 0.5)
}

grid_search = GridSearchCV(pipe, parameters, cv=5, n_jobs=4, verbose=1)
grid_search.fit(X=x_train, y=y_train)

Checking the shape of the matrices confirms that x_train and y_train have the same length (the number of rows in both = 3269). So I'm confused as to why fitting the grid search gives me the following error:

Fitting 5 folds for each of 4 candidates, totalling 20 fits
[Parallel(n_jobs=4)]: Using backend LokyBackend with 4 concurrent workers.
[Parallel(n_jobs=4)]: Done  20 out of  20 | elapsed:    2.0s finished
--------------------
ValueErrorTraceback (most recent call last)
<ipython-input-18-4e85850d6599> in <module>
      29 grid_search = GridSearchCV(pipe, parameters, cv=5, n_jobs=4, verbose=1)
----> 30 grid_search.fit(X=x_train, y=y_train)

........................................

ValueError: Number of labels=3269 does not match number of samples=2

What does it mean by number of labels and samples? There should be 3269 samples, since the shape of both X and y matrices is (3269, 2) and (3269, ), respectively.

Any help is super appreciated! Let me know if the full traceback would help, but it was extremely long so I didn't include it.

Answer 1

Try:

from sklearn.model_selection import train_test_split, GridSearchCV
from sklearn.pipeline import Pipeline
from sklearn.ensemble import RandomForestClassifier
from sklearn.feature_extraction.text import TfidfVectorizer

# features = ['description']
# target = 'ratingCategory'
x_train, x_val, y_train, y_val = train_test_split(
    # train[features],
    train.description,
    # train[target],
    train.ratingCategory,
    test_size=0.2,
    # stratify=train[target],
    stratify=train.ratingCategory,
    random_state=95
)

vect = TfidfVectorizer()
clf = RandomForestClassifier()

pipe = Pipeline([
    ('vect', vect), 
    ('clf', clf)]
)

parameters = {
    'vect__min_df': (0.01, 0.05),
    'clf__ccp_alpha': (0.1, 0.5)
}

grid_search = GridSearchCV(pipe, parameters, cv=5, n_jobs=4, verbose=1)
grid_search.fit(X=x_train, y=y_train)