Machine Learning snippets

I'm learning ML and those are code snippets that are useful for me. Contributions are welcomed!

Basics

Imports

%matplotlib inline
import pandas as pd
import seaborn as sns
import matplotlib.pyplot as plt
import numpy as np
from sklearn.model_selection import train_test_split
import re, json
from scipy import stats
from sklearn.metrics import accuracy_score, f1_score, confusion_matrix, recall_score
%config InlineBackend.figure_format = "retina"
plt.rcParams["figure.figsize"] = [15, 8]

Mapping rows

def transform_row(row):
    row["new_column"] = np.log(row["old_column"])
    row["another_column"] = np.mean(row["old_column"])
    return row

df = df.apply(transform_row, axis=1)

Mapping column

df["fresh_column"] = df["old_column"].map(lambda x: np.log(x) if x > 0 else 0)

Merging by column

new_df = pd.merge(left=df_1, right=df_2, left_on=df_1_column, right_on=df_2_column)

Merging by appending

new_df = df_1.append(df_2, sort=False, ignore_index=True)

Dropping colums

new_df = df.drop(columns=["name"])

# or

df.drop(columns=["name"], inplace=True)

Checking for missing values

def show_missing(data, top=20):
    total = data.isnull().sum()
    percent = (data.isnull().sum()/data.isnull().count())
    missing_data = pd.concat([total, percent, data.dtypes], 
        axis=1, keys=['Total', 'Percent', 'Type'])
    missing_data = missing_data.sort_values('Total', ascending=False)
    return missing_data.head(top)

Checking values

df["column"].describe() # scalars
df["column"].value_counts() # categorical

Drawing

Distribution

def draw_dist(data, x, hue):
    from scipy.stats import norm
    fig, axes = plt.subplots(nrows=1, ncols=1,figsize=(15, 8))
    ax = sns.distplot(
        data[data[hue]==1][x].dropna(),
        bins=20,
        label = hue,
        ax = axes,
        kde = False,
        fit = norm
    )
    ax.legend()
    ax = sns.distplot(
        data[data[hue]==0][x].dropna(), 
        bins=20, 
        label = 'not ' + hue, 
        ax = axes, 
        kde = False,
        fit = norm
    )
    ax.legend()

draw_dist(df, "amount", "fraud") # Usage

Swarm

Works best if x has less than 4 values.

def draw_swarm(data, x, y, hue):
    fig, axes = plt.subplots(nrows=1, ncols=1,figsize=(15, 8))
    sns.swarmplot(x=x, y=y, data=data, hue=hue, ax=axes)

draw_swarm(df, "age", "amount", "fraud") # Usage

Count

Works best if x has few values.

def draw_count(data, x, hue):
    fig, axes = plt.subplots(nrows=1, ncols=1,figsize=(15, 8))
    sns.countplot(x = x, hue = hue, data = data, ax=axes)

draw_count(df, "age", "fraud")

Correlation

Hierarchy shows what features are redundant.

def draw_corr(df):
    corr = df.corr()
    mask = np.zeros_like(corr, dtype=np.bool)
    mask[np.triu_indices_from(mask)] = True
    f, ax = plt.subplots(figsize=(15, 8))
    cmap = sns.diverging_palette(220, 10, as_cmap=True)
    sns.heatmap(corr, mask=mask, cmap=cmap, vmax=.3, center=0,
                square=True, linewidths=.5, cbar_kws={"shrink": .5})

def draw_corr_with_hierarchy(df):
    sns.clustermap(df.corr())

Feature importance

def get_importance(data, model):
    fi = {
        'Features': data.columns.to_list(), 
        'Importance': model.feature_importances_
    }
    return pd.DataFrame(fi, index=None).sort_values('Importance', ascending=False)

def draw_importance(data, model):
    importance = get_importance(data, model)
    sns.barplot(y=importance.Features, x=importance.Importance)

# Usage
m = clf.fit(X, y)
draw_importance(X, m)

Feature modeling

Fixing missing values

df["column"] = df["column"].fillna("value")
# or
df.loc[df["column"].isnull(), ["column"]] = "value"

Fixing skewness

def fix_skewed(data, target_column = None):
    from scipy.stats import skew

    numeric = data.dtypes[data.dtypes != "object"].index.to_list()
   
    if target_column is not None:
        numeric.remove(target_column)

    skewed_feats = data[numeric].apply(lambda x: skew(x.dropna()))
    skewed_feats = skewed_feats[skewed_feats > 0.75]
    skewed_feats = skewed_feats.index

    data[skewed_feats] = np.log1p(data[skewed_feats])
    return data

Watch out for negative values in column. If column has negative values, you can try fixing it by applying np.cbrt insted np.log1p.

If you fix skewness of targeted column, remember to apply np.expm1 after predictions to reverse np.log1p.

Dropping not important features

def drop_not_important(df, m, alpha = 0.05):
    importance = get_importance(df, m)
    to_keep = importance[importance.Importance > alpha].Features
    return df[to_keep]

Dropping outliers

Useful when there are small number of outliers. Don't do it, if you have unbalanced data. You might delete data that is already scarse.

def get_outliers(data, column):
    from scipy import stats
    z = np.abs(stats.zscore(data[column]))
    return np.where(z > 3)[0].tolist()

def drop_outliers(data, column):
    outliers = get_outliers(data, column)
    
    if len(outliers) < 0:
        return data
    else:
        return data.drop(outliers).reset_index(drop=True)

Upsampling

Useful when categories are unbalanced. Remember to split train & test before upsampling.

def upsample(df, column):
    from sklearn.utils import resample
    cons = df[df[column]==0]
    pros = df[df[column]==1]
    pros_upsampled = resample(pros, replace=True, n_samples=len(cons))

    return pd.concat([cons, pros_upsampled])

# Usage
train, test = train_test_split(data, test_size=0.33, random_state=42)
upsampled_train = upsample(train, "column")

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