Author: Dmitry Sergeyev, Zeptolab. This material is subject to the terms and conditions of the Creative Commons CC BY-NC-SA 4.0 license. Free use is permitted for any non-commercial purpose.

Prior to working on the assignment, you'd better check out the corresponding course material:

- Time series analysis with Python, the same as an interactive web-based Kaggle Kernel
- Predicting future with Facebook Prophet, the same as a Kaggle Kernel

You can also practice with demo assignments, which are simpler and already shared with solutions:

- "Time series analysis": assignment + solution

Also, checkout mlcourse.ai video lecture on time series

- write code and perform computations in the cells below
- choose answers in the webform. Solutions will be shared only with those who've filled in this form

In [1]:

```
# importing necessary libraries
import warnings
warnings.filterwarnings('ignore')
import random
random.seed(42)
import pandas as pd
import numpy as np
from sklearn.linear_model import LinearRegression, RidgeCV, LassoCV
from sklearn.metrics import mean_absolute_error, mean_squared_error
from sklearn.preprocessing import StandardScaler
from sklearn.model_selection import TimeSeriesSplit, cross_val_score
import matplotlib.pyplot as plt
import seaborn as sns; sns.set()
%config InlineBackend.figure_format = 'retina'
```

We will take real time-series data of total ads watched by hour in one of our games. It's stored in the course repo.

In [2]:

```
df = pd.read_csv('../../data/ads_hour.csv',
index_col=['Date'], parse_dates=['Date'])
```

In [3]:

```
with plt.style.context('bmh'):
plt.figure(figsize=(15, 8))
plt.title('Ads watched (hour ticks)')
plt.plot(df.ads);
```

We have everything you could ask for - trend, seasonality, even some outliers.

In this assignment we will concentrate on methods that have proven to be working in practice and can provide quality, comparable to ARIMA models. Namely, feature engineering, selecting and machine learning

But before digging into practice - a tiny bit of theory on how to create even more features. In this hometask we will be working with linear models. That means we assume there's a linear dependance between our target variable and the featureset, and we try to model that dependance. Now remember the `hour`

variable we've created in the lecture? That variable showed on which hour a given observation arrived. Naturally, we expect hour plays a huge role, since at night the amount ofactive users who can watch ads drops significantly, at during the day it rises to its peak. However, if we use a single feature with number of an hour, linear models will not be able to model that dependance correctly. Why? Because look at the feature itself. It has values from $0$ to $23$ and even though we know that 0:00 is closer to 23:00 than, say, 20:00 to 23:00, the model will only see the numbers, not the logic behind them. And, of course, number 0 is way further from number 23 than number 20 from 23.

How will we solve that problem?

First possible solution - let's get dummies and make 24 new columns out of one. Clear disadvantages - we explode the dimentionality of our data and lose any trace of the cyclical nature of hours.

Second solution - sine/cosine transformation. To fully understand that approach, read this short article. But in short - we want to encode hour feature with two new columns, which are sine and cosine transformations of "hour from midnight"

We will use the already familiar `prepareData`

function with some modifications - sine/cosine transformation for `hour`

and dummy transformation for `weekday`

features

In [4]:

```
def prepareData(data, lag_start=5, lag_end=14, test_size=0.15):
"""
series: pd.DataFrame
dataframe with timeseries
lag_start: int
initial step back in time to slice target variable
example - lag_start = 1 means that the model
will see yesterday's values to predict today
lag_end: int
final step back in time to slice target variable
example - lag_end = 4 means that the model
will see up to 4 days back in time to predict today
test_size: float
size of the test dataset after train/test split as percentage of dataset
"""
data = pd.DataFrame(data.copy())
data.columns = ["y"]
# calculate test index start position to split data on train test
test_index = int(len(data) * (1 - test_size))
# adding lags of original time series data as features
for i in range(lag_start, lag_end):
data["lag_{}".format(i)] = data.y.shift(i)
# transforming df index to datetime and creating new variables
data.index = pd.to_datetime(data.index)
data["hour"] = data.index.hour
data["weekday"] = data.index.weekday
# since we will be using only linear models we need to get dummies from weekdays
# to avoid imposing weird algebraic rules on day numbers
data = pd.concat([
data.drop("weekday", axis=1),
pd.get_dummies(data['weekday'], prefix='weekday')
], axis=1)
# encode hour with sin/cos transformation
# credits - https://ianlondon.github.io/blog/encoding-cyclical-features-24hour-time/
data['sin_hour'] = np.sin(2*np.pi*data['hour']/24)
data['cos_hour'] = np.cos(2*np.pi*data['hour']/24)
data.drop(["hour"], axis=1, inplace=True)
data = data.dropna()
data = data.reset_index(drop=True)
# splitting whole dataset on train and test
X_train = data.loc[:test_index].drop(["y"], axis=1)
y_train = data.loc[:test_index]["y"]
X_test = data.loc[test_index:].drop(["y"], axis=1)
y_test = data.loc[test_index:]["y"]
return X_train, X_test, y_train, y_test
```

Use the functions on original `df`

to prepare datasets necessary for model training. Reserve 30% of data for testing, use initial lag 12 and final lag 48. This way the model will be able to make forecasts twelve steps ahead, having observed data from the previous 1.5 day.

Scale the resulting datasets with the help of `StandardScaler`

and create new variables - `X_train_scaled`

and `X_test_scaled`

. Don't forget that `scaler`

should be trained on train set only to prevent information about future from leaking.

In [5]:

```
# You code here
# X_train, X_test, y_train, y_test =
```

Now train a simple linear regression on scaled data:

In [6]:

```
# You code here
```

Check the quality of the model on the training set via cross-validation. To do so you need to create an object-generator of time series cv folds with the help of `TimeSeriesSplit`

. Set the number of folds to be equal to 5. Then use `cross_val_score`

, feeding it's `cv`

parameter with the created generator. Quality metrics should be `neg_mean_absolute_error`

.

Don't forget to take an average of the result and multiply it by -1.

In [7]:

```
# You code here
# tscv =
```

**Question 1. What is the value of MAE on cross-validation?**

*For discussions, please stick to ODS Slack, channel #mlcourse_ai_news, pinned thread #a4_fall2019*

- 4876
- 41454725
- 4490
- 0.712

Now let's have a look at the forecast itself. We'll need `plotModelResults`

function.

In [8]:

```
def mean_absolute_percentage_error(y_true, y_pred):
return np.mean(np.abs((y_true - y_pred) / y_true)) * 100
```

In [ ]:

```
def plotModelResults(model, df_train, df_test, y_train, y_test, plot_intervals=False, scale=1.96, cv=tscv):
"""
Plots modelled vs fact values
model: fitted model
df_train, df_test: splitted featuresets
y_train, y_test: targets
plot_intervals: bool, if True, plot prediction intervals
scale: float, sets the width of the intervals
cv: cross validation method, needed for intervals
"""
# making predictions for test
prediction = model.predict(df_test)
plt.figure(figsize=(20, 7))
plt.plot(prediction, "g", label="prediction", linewidth=2.0)
plt.plot(y_test.values, label="actual", linewidth=2.0)
if plot_intervals:
# calculate cv scores
cv = cross_val_score(
model,
df_train,
y_train,
cv=cv,
scoring="neg_mean_squared_error"
)
# calculate cv error deviation
deviation = np.sqrt(cv.std())
# calculate lower and upper intervals
lower = prediction - (scale * deviation)
upper = prediction + (scale * deviation)
plt.plot(lower, "r--", label="upper bond / lower bond", alpha=0.5)
plt.plot(upper, "r--", alpha=0.5)
# calculate overall quality on test set
mae = mean_absolute_error(prediction, y_test)
mape = mean_absolute_percentage_error(prediction, y_test)
plt.title("MAE {}, MAPE {}%".format(round(mae), round(mape, 2)))
plt.legend(loc="best")
plt.grid(True);
```

For model coefficients visualization use the following functions:

In [10]:

```
def getCoefficients(model):
"""Returns sorted coefficient values of the model"""
coefs = pd.DataFrame(model.coef_, X_train.columns)
coefs.columns = ["coef"]
coefs["abs"] = coefs.coef.apply(np.abs)
return coefs.sort_values(by="abs", ascending=False).drop(["abs"], axis=1)
def plotCoefficients(model):
"""Plots sorted coefficient values of the model"""
coefs = getCoefficients(model)
plt.figure(figsize=(20, 7))
coefs.coef.plot(kind='bar')
plt.grid(True, axis='y')
plt.hlines(y=0, xmin=0, xmax=len(coefs), linestyles='dashed')
plt.show()
```

Check the model results and plot the coefficients

In [11]:

```
# You code here
```

Wonderful, the intervals are plotted, forecast quality is great and everything seems to be fine, but...We might be having too many variables in our model and, possibly, some of them are not that important and can be dropped, reducing the dimentionality of data and reducing the chances of overfit. To make sure we have extra features, plot a heatmape of `X_train`

data correlations with the help of `heatmap`

function from `seaborn`

library:

Indeed, features are highly correlated and you can even observe some kind of "seasonality" in those correlations on each 24-th lag. Let's try to add regularization to our models and remove some features.

Train Lasso regression on cross-validation (`LassoCV`

) again feeding the `cv`

parameter with the created generator-object.

Plot the forecast of the model and notice that the error on test dataset has not increased significantly

In [12]:

```
# You code here
```

Perfect, we are still having practically the same model quality, while having less features. Use the function `getCoefficients`

and find, how many features are now dropped (coefficient equals zero).

In [13]:

```
# You code here
```

**Question 2. How many coefficients of Lasso model equal zero? (with 6 digit precision)?**

*For discussions, please stick to ODS Slack, channel #mlcourse_ai_news, pinned thread #a4_fall2019*

- 11
- 12
- 15
- 17

Alright, we have some features dropped. But what if we want to go further and transform our linear-dependant features into more compact representation? To do so we'll use principal component analysis.

In [14]:

```
from sklearn.decomposition import PCA
from sklearn.pipeline import make_pipeline
def plotPCA(pca):
"""
Plots accumulated percentage of explained variance by component
pca: fitted PCA object
"""
components = range(1, pca.n_components_ + 1)
variance = np.cumsum(np.round(pca.explained_variance_ratio_, decimals=4)*100)
plt.figure(figsize=(20, 10))
plt.bar(components, variance)
# additionally mark the level of 95% of explained variance
plt.hlines(y = 95, xmin=0, xmax=len(components), linestyles='dashed', colors='red')
plt.xlabel('PCA components')
plt.ylabel('variance')
plt.xticks(components)
plt.show()
```

In [15]:

```
# Create PCA object: pca
# Train PCA on scaled data
# plot explained variance
```

**Question 3. What is the minimal number of components needed to explain at least 95% of variance of the train dataset?**

*For discussions, please stick to ODS Slack, channel #mlcourse_ai_news, pinned thread #a4_fall2019*

- 5
- 7
- 9
- 12

Create the `pca`

object once again, this time setting inside it the optimal number of components (explaining at least 95% of variance). After that create two new variables - `pca_features_train`

and `pca_features_test`

, assigning to them pca-transformed scaled datasets.

In [16]:

```
# You code here
```

Now train linear regression on pca features and plot its forecast.

In [17]:

```
# You code here
```

**Question 4. What is the MAE of linear regression, trained on pca-transformed features?**

*For discussions, please stick to ODS Slack, channel #mlcourse_ai_news, pinned thread #a4_fall2019*

- 5140
- 4917
- 6719
- 4663