# Getting Started¶

## Basic usage¶

### Automatic cross-validation¶

Surprise has a set of built-in algorithms and datasets for you to play with. In its simplest form, it only takes a few lines of code to run a cross-validation procedure:

From file examples/basic_usage.py
from surprise import SVD
from surprise import Dataset
from surprise.model_selection import cross_validate

# We'll use the famous SVD algorithm.
algo = SVD()

# Run 5-fold cross-validation and print results
cross_validate(algo, data, measures=['RMSE', 'MAE'], cv=5, verbose=True)


The result should be as follows (actual values may vary due to randomization):

Evaluating RMSE, MAE of algorithm SVD on 5 split(s).

Fold 1  Fold 2  Fold 3  Fold 4  Fold 5  Mean    Std
RMSE        0.9311  0.9370  0.9320  0.9317  0.9391  0.9342  0.0032
MAE         0.7350  0.7375  0.7341  0.7342  0.7375  0.7357  0.0015
Fit time    6.53    7.11    7.23    7.15    3.99    6.40    1.23
Test time   0.26    0.26    0.25    0.15    0.13    0.21    0.06


The load_builtin() method will offer to download the movielens-100k dataset if it has not already been downloaded, and it will save it in the .surprise_data folder in your home directory (you can also choose to save it somewhere else).

We are here using the well-known SVD algorithm, but many other algorithms are available. See Using prediction algorithms for more details.

The cross_validate() function runs a cross-validation procedure according to the cv argument, and computes some accuracy measures. We are here using a classical 5-fold cross-validation, but fancier iterators can be used (see here).

### Train-test split and the fit() method¶

If you don’t want to run a full cross-validation procedure, you can use the train_test_split() to sample a trainset and a testset with given sizes, and use the accuracy metric of your chosing. You’ll need to use the fit() method which will train the algorithm on the trainset, and the test() method which will return the predictions made from the testset:

From file examples/train_test_split.py
from surprise import SVD
from surprise import Dataset
from surprise import accuracy
from surprise.model_selection import train_test_split

# sample random trainset and testset
# test set is made of 25% of the ratings.
trainset, testset = train_test_split(data, test_size=.25)

# We'll use the famous SVD algorithm.
algo = SVD()

# Train the algorithm on the trainset, and predict ratings for the testset
algo.fit(trainset)
predictions = algo.test(testset)

# Then compute RMSE
accuracy.rmse(predictions)


Result:

RMSE: 0.9411


Note that you can train and test an algorithm with the following one-line:

predictions = algo.fit(trainset).test(testset)


In some cases, your trainset and testset are already defined by some files. Please refer to this section to handle such cases.

### Train on a whole trainset and the predict() method¶

Obviously, we could also simply fit our algorithm to the whole dataset, rather than running cross-validation. This can be done by using the build_full_trainset() method which will build a trainset object:

From file examples/predict_ratings.py
from surprise import KNNBasic
from surprise import Dataset

# Load the movielens-100k dataset

# Retrieve the trainset.
trainset = data.build_full_trainset()

# Build an algorithm, and train it.
algo = KNNBasic()
algo.fit(trainset)


We can now predict ratings by directly calling the predict() method. Let’s say you’re interested in user 196 and item 302 (make sure they’re in the trainset!), and you know that the true rating $$r_{ui} = 4$$:

From file examples/predict_ratings.py
uid = str(196)  # raw user id (as in the ratings file). They are **strings**!
iid = str(302)  # raw item id (as in the ratings file). They are **strings**!

# get a prediction for specific users and items.
pred = algo.predict(uid, iid, r_ui=4, verbose=True)


The result should be:

user: 196        item: 302        r_ui = 4.00   est = 4.06   {'actual_k': 40, 'was_impossible': False}


Note

The predict() uses raw ids (please read this about raw and inner ids). As the dataset we have used has been read from a file, the raw ids are strings (even if they represent numbers).

We have so far used a built-in dataset, but you can of course use your own. This is explained in the next section.

## Use a custom dataset¶

Surprise has a set of builtin datasets, but you can of course use a custom dataset. Loading a rating dataset can be done either from a file (e.g. a csv file), or from a pandas dataframe. Either way, you will need to define a Reader object for Surprise to be able to parse the file or the dataframe.

• To load a dataset from a file (e.g. a csv file), you will need the load_from_file() method:

From file examples/load_custom_dataset.py
from surprise import BaselineOnly
from surprise import Dataset
from surprise import Reader
from surprise.model_selection import cross_validate

# path to dataset file
file_path = os.path.expanduser('~/.surprise_data/ml-100k/ml-100k/u.data')

# As we're loading a custom dataset, we need to define a reader. In the
# movielens-100k dataset, each line has the following format:
# 'user item rating timestamp', separated by '\t' characters.
reader = Reader(line_format='user item rating timestamp', sep='\t')

# We can now use this dataset as we please, e.g. calling cross_validate
cross_validate(BaselineOnly(), data, verbose=True)


For more details about readers and how to use them, see the Reader class documentation.

Note

As you already know from the previous section, the Movielens-100k dataset is built-in so a much quicker way to load the dataset is to do data = Dataset.load_builtin('ml-100k'). We will of course ignore this here.

• To load a dataset from a pandas dataframe, you will need the load_from_df() method. You will also need a Reader object, but only the rating_scale parameter must be specified. The dataframe must have three columns, corresponding to the user (raw) ids, the item (raw) ids, and the ratings in this order. Each row thus corresponds to a given rating. This is not restrictive as you can reorder the columns of your dataframe easily.

From file examples/load_from_dataframe.py
import pandas as pd

from surprise import NormalPredictor
from surprise import Dataset
from surprise.model_selection import cross_validate

# Creation of the dataframe. Column names are irrelevant.
ratings_dict = {'itemID': [1, 1, 1, 2, 2],
'userID': [9, 32, 2, 45, 'user_foo'],
'rating': [3, 2, 4, 3, 1]}
df = pd.DataFrame(ratings_dict)

# The columns must correspond to user id, item id and ratings (in that order).
data = Dataset.load_from_df(df[['userID', 'itemID', 'rating']],
rating_scale=(1, 5))

# We can now use this dataset as we please, e.g. calling cross_validate
cross_validate(NormalPredictor(), data, cv=2)


The dataframe initially looks like this:

      itemID  rating    userID
0       1       3         9
1       1       2        32
2       1       4         2
3       2       3        45
4       2       1  user_foo


## Use cross-validation iterators¶

For cross-validation, we can use the cross_validate() function that does all the hard work for us. But for a better control, we can also instanciate a cross-validation iterator, and make predictions over each split using the split() method of the iterator, and the test() method of the algorithm. Here is an example where we use a classical K-fold cross-validation procedure with 3 splits:

From file examples/use_cross_validation_iterators.py
from surprise import SVD
from surprise import Dataset
from surprise import accuracy
from surprise.model_selection import KFold

# Load the movielens-100k dataset

# define a cross-validation iterator
kf = KFold(n_splits=3)

algo = SVD()

for trainset, testset in kf.split(data):

# train and test algorithm.
algo.fit(trainset)
predictions = algo.test(testset)

# Compute and print Root Mean Squared Error
accuracy.rmse(predictions, verbose=True)


Result could be, e.g.:

RMSE: 0.9374
RMSE: 0.9476
RMSE: 0.9478


Other cross-validation iterator can be used, like LeaveOneOut or ShuffleSplit. See all the available iterators here. The design of Surprise’s cross-validation tools is heavily inspired from the excellent scikit-learn API.

A special case of cross-validation is when the folds are already predefined by some files. For instance, the movielens-100K dataset already provides 5 train and test files (u1.base, u1.test … u5.base, u5.test). Surprise can handle this case by using a surprise.model_selection.split.PredefinedKFold object:

From file examples/load_custom_dataset_predefined_folds.py
from surprise import SVD
from surprise import Dataset
from surprise import Reader
from surprise import accuracy
from surprise.model_selection import PredefinedKFold

# path to dataset folder
files_dir = os.path.expanduser('~/.surprise_data/ml-100k/ml-100k/')

# This time, we'll use the built-in reader.

# folds_files is a list of tuples containing file paths:
# [(u1.base, u1.test), (u2.base, u2.test), ... (u5.base, u5.test)]
train_file = files_dir + 'u%d.base'
test_file = files_dir + 'u%d.test'
folds_files = [(train_file % i, test_file % i) for i in (1, 2, 3, 4, 5)]

pkf = PredefinedKFold()

algo = SVD()

for trainset, testset in pkf.split(data):

# train and test algorithm.
algo.fit(trainset)
predictions = algo.test(testset)

# Compute and print Root Mean Squared Error
accuracy.rmse(predictions, verbose=True)


Of course, nothing prevents you from only loading a single file for training and a single file for testing. However, the folds_files parameter still needs to be a list.

## Tune algorithm parameters with GridSearchCV¶

The cross_validate() function reports accuracy metric over a cross-validation procedure for a given set of parameters. If you want to know which parameter combination yields the best results, the GridSearchCV class comes to the rescue. Given a dict of parameters, this class exhaustively tries all the combinations of parameters and reports the best parameters for any accuracy measure (averaged over the different splits). It is heavily inspired from scikit-learn’s GridSearchCV.

Here is an example where we try different values for parameters n_epochs, lr_all and reg_all of the SVD algorithm.

From file examples/grid_search_usage.py
from surprise import SVD
from surprise import Dataset
from surprise.model_selection import GridSearchCV

# Use movielens-100K

param_grid = {'n_epochs': [5, 10], 'lr_all': [0.002, 0.005],
'reg_all': [0.4, 0.6]}
gs = GridSearchCV(SVD, param_grid, measures=['rmse', 'mae'], cv=3)

gs.fit(data)

# best RMSE score
print(gs.best_score['rmse'])

# combination of parameters that gave the best RMSE score
print(gs.best_params['rmse'])


Result:

0.961300130118
{'n_epochs': 10, 'lr_all': 0.005, 'reg_all': 0.4}


We are here evaluating the average RMSE and MAE over a 3-fold cross-validation procedure, but any cross-validation iterator can used.

Once fit() has been called, the best_estimator attribute gives us an algorithm instance with the optimal set of parameters, which can be used how we please:

From file examples/grid_search_usage.py
# We can now use the algorithm that yields the best rmse:
algo = gs.best_estimator['rmse']
algo.fit(data.build_full_trainset())


Note

Dictionary parameters such as bsl_options and sim_options require particular treatment. See usage example below:

param_grid = {'k': [10, 20],
'sim_options': {'name': ['msd', 'cosine'],
'min_support': [1, 5],
'user_based': [False]}
}


Naturally, both can be combined, for example for the KNNBaseline algorithm:

param_grid = {'bsl_options': {'method': ['als', 'sgd'],
'reg': [1, 2]},
'k': [2, 3],
'sim_options': {'name': ['msd', 'cosine'],
'min_support': [1, 5],
'user_based': [False]}
}


For further analysis, the cv_results attribute has all the needed information and can be imported in a pandas dataframe:

From file examples/grid_search_usage.py
results_df = pd.DataFrame.from_dict(gs.cv_results)


In our example, the cv_results attribute looks like this (floats are formatted):

'split0_test_rmse': [1.0, 1.0, 0.97, 0.98, 0.98, 0.99, 0.96, 0.97]
'split1_test_rmse': [1.0, 1.0, 0.97, 0.98, 0.98, 0.99, 0.96, 0.97]
'split2_test_rmse': [1.0, 1.0, 0.97, 0.98, 0.98, 0.99, 0.96, 0.97]
'mean_test_rmse':   [1.0, 1.0, 0.97, 0.98, 0.98, 0.99, 0.96, 0.97]
'std_test_rmse':    [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
'rank_test_rmse':   [7 8 3 5 4 6 1 2]
'split0_test_mae':  [0.81, 0.82, 0.78, 0.79, 0.79, 0.8, 0.77, 0.79]
'split1_test_mae':  [0.8, 0.81, 0.78, 0.79, 0.78, 0.79, 0.77, 0.78]
'split2_test_mae':  [0.81, 0.81, 0.78, 0.79, 0.78, 0.8, 0.77, 0.78]
'mean_test_mae':    [0.81, 0.81, 0.78, 0.79, 0.79, 0.8, 0.77, 0.78]
'std_test_mae':     [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
'rank_test_mae':    [7 8 2 5 4 6 1 3]
'mean_fit_time':    [1.53, 1.52, 1.53, 1.53, 3.04, 3.05, 3.06, 3.02]
'std_fit_time':     [0.03, 0.04, 0.0, 0.01, 0.04, 0.01, 0.06, 0.01]
'mean_test_time':   [0.46, 0.45, 0.44, 0.44, 0.47, 0.49, 0.46, 0.34]
'std_test_time':    [0.0, 0.01, 0.01, 0.0, 0.03, 0.06, 0.01, 0.08]
'params':           [{'n_epochs': 5, 'lr_all': 0.002, 'reg_all': 0.4}, {'n_epochs': 5, 'lr_all': 0.002, 'reg_all': 0.6}, {'n_epochs': 5, 'lr_all': 0.005, 'reg_all': 0.4}, {'n_epochs': 5, 'lr_all': 0.005, 'reg_all': 0.6}, {'n_epochs': 10, 'lr_all': 0.002, 'reg_all': 0.4}, {'n_epochs': 10, 'lr_all': 0.002, 'reg_all': 0.6}, {'n_epochs': 10, 'lr_all': 0.005, 'reg_all': 0.4}, {'n_epochs': 10, 'lr_all': 0.005, 'reg_all': 0.6}]
'param_n_epochs':   [5, 5, 5, 5, 10, 10, 10, 10]
'param_lr_all':     [0.0, 0.0, 0.01, 0.01, 0.0, 0.0, 0.01, 0.01]
'param_reg_all':    [0.4, 0.6, 0.4, 0.6, 0.4, 0.6, 0.4, 0.6]


As you can see, each list has the same size of the number of parameter combination. It corresponds to the following table:

split0_test_rmse split1_test_rmse split2_test_rmse mean_test_rmse std_test_rmse rank_test_rmse split0_test_mae split1_test_mae split2_test_mae mean_test_mae std_test_mae rank_test_mae mean_fit_time std_fit_time mean_test_time std_test_time params param_n_epochs param_lr_all param_reg_all
0.99775 0.997744 0.996378 0.997291 0.000645508 7 0.807862 0.804626 0.805282 0.805923 0.00139657 7 1.53341 0.0305216 0.455831 0.000922113 {‘n_epochs’: 5, ‘lr_all’: 0.002, ‘reg_all’: 0.4} 5 0.002 0.4
1.00381 1.00304 1.00257 1.00314 0.000508358 8 0.816559 0.812905 0.813772 0.814412 0.00155866 8 1.5199 0.0367117 0.451068 0.00938646 {‘n_epochs’: 5, ‘lr_all’: 0.002, ‘reg_all’: 0.6} 5 0.002 0.6
0.973524 0.973595 0.972495 0.973205 0.000502609 3 0.783361 0.780242 0.78067 0.781424 0.00138049 2 1.53449 0.00496203 0.441558 0.00529696 {‘n_epochs’: 5, ‘lr_all’: 0.005, ‘reg_all’: 0.4} 5 0.005 0.4
0.98229 0.982059 0.981486 0.981945 0.000338056 5 0.794481 0.790781 0.79186 0.792374 0.00155377 5 1.52739 0.00859185 0.44463 0.000888907 {‘n_epochs’: 5, ‘lr_all’: 0.005, ‘reg_all’: 0.6} 5 0.005 0.6
0.978034 0.978407 0.976919 0.977787 0.000632049 4 0.787643 0.784723 0.784957 0.785774 0.00132486 4 3.03572 0.0431101 0.466606 0.0254965 {‘n_epochs’: 10, ‘lr_all’: 0.002, ‘reg_all’: 0.4} 10 0.002 0.4
0.986263 0.985817 0.985004 0.985695 0.000520899 6 0.798218 0.794457 0.795373 0.796016 0.00160135 6 3.0544 0.00636185 0.488357 0.0576194 {‘n_epochs’: 10, ‘lr_all’: 0.002, ‘reg_all’: 0.6} 10 0.002 0.6
0.963751 0.963463 0.962676 0.963297 0.000454661 1 0.774036 0.770548 0.771588 0.772057 0.00146201 1 3.0636 0.0597982 0.456484 0.00510321 {‘n_epochs’: 10, ‘lr_all’: 0.005, ‘reg_all’: 0.4} 10 0.005 0.4
0.973605 0.972868 0.972765 0.973079 0.000374222 2 0.78607 0.781918 0.783537 0.783842 0.00170855 3 3.01907 0.011834 0.338839 0.075346 {‘n_epochs’: 10, ‘lr_all’: 0.005, ‘reg_all’: 0.6} 10 0.005 0.6

## Command line usage¶

Surprise can also be used from the command line, for example:

surprise -algo SVD -params "{'n_epochs': 5, 'verbose': True}" -load-builtin ml-100k -n-folds 3


See detailed usage by running:

surprise -h