Basic Exploratory Data Analysis with Python


import pandas as pd
import numpy as np


df = pd.read_csv(path)

! pip install seaborn
import matplotlib.pyplot as plt
import seaborn as sns

# list the data types for each column

# correlation between the variable

# correlation between three specific variable
df[['bore','stroke' ,'compression-ratio','horsepower']].corr()

# scatterplot of "engine-size" and "price"
sns.regplot(x="engine-size", y="price", data=df)

# correlation between the two
df[["engine-size", "price"]].corr()

# scatterplot and correlation between highway-mpg and price
sns.regplot(x="highway-mpg", y="price", data=df)
df[['highway-mpg', 'price']].corr()

# boxplots for price for each body-style
sns.boxplot(x="body-style", y="price", data=df)

# boxplots for price for each engine-location
sns.boxplot(x="engine-location", y="price", data=df)

# find out basic statistical analysis
df.describe()    # only numeric fields
df.describe(include=['object'])    # with object fields

# value counts of a field
df['drive-wheels'].value_counts().to_frame()    # in table

# make a cross table for engine-location count
# engine-location as variable
engine_loc_counts = df['engine-location'].value_counts().to_frame()
engine_loc_counts.rename(columns={'engine-location': 'value_counts'}, inplace=True) = 'engine-location'


df['drive-wheels'].unique()   # different drive-wheels

df_group_one = df[['drive-wheels','price']].groupby(['drive-wheels'],as_index=False).mean()
df_group_one    # price for drive-wheels

df_gptest = df[['drive-wheels','body-style','price']]
grouped_test1 = df_gptest.groupby(['drive-wheels','body-style'],as_index=False).mean()
grouped_test1    # price for drive-wheels and body-style

grouped_pivot = grouped_test1.pivot(index='drive-wheels',columns='body-style')
grouped_pivot    # pivot for better reading


plt.pcolor(grouped_pivot, cmap='RdBu')    # use the grouped results

# redo with the correct axis values
fig, ax = plt.subplots()
im = ax.pcolor(grouped_pivot, cmap='RdBu')
row_labels = grouped_pivot.columns.levels[1]     #label names
col_labels = grouped_pivot.index    #label names
#move ticks and labels to the center
ax.set_xticks(np.arange(grouped_pivot.shape[1]) + 0.5, minor=False)
ax.set_yticks(np.arange(grouped_pivot.shape[0]) + 0.5, minor=False)
ax.set_xticklabels(row_labels, minor=False)     #insert labels
ax.set_yticklabels(col_labels, minor=False)     #insert labels
plt.xticks(rotation=90)    #rotate label if too long


# By convention, when the
# p-value is  <  0.001: we say there is strong evidence that the correlation is significant.
# p-value is  <  0.05: there is moderate evidence that the correlation is significant.
# p-value is  <  0.1: there is weak evidence that the correlation is significant.
# p-value is  >  0.1: there is no evidence that the correlation is significant.

from scipy import stats

# horsepower vs price
pearson_coef, p_value = stats.pearsonr(df['horsepower'], df['price'])
print("The Pearson Correlation Coefficient is", pearson_coef, " with a P-value of P = ", p_value)
# Since the p-value is  <  0.001, the correlation between horsepower and price is statistically significant, and the linear relationship is quite strong (~0.809, close to 1)

# ANOVA: Analysis of Variance
# The Analysis of Variance (ANOVA) is a statistical method used to test whether there are significant differences between the means of two or more groups. ANOVA returns two parameters:
# F-test score: ANOVA assumes the means of all groups are the same, calculates how much the actual means deviate from the assumption, and reports it as the F-test score. A larger score means there is a larger difference between the means.
# P-value: P-value tells how statistically significant is our calculated score value.
# If our price variable is strongly correlated with the variable we are analyzing, expect ANOVA to return a sizeable F-test score and a small p-value.

# price for wheel-drive
f_val, p_val = stats.f_oneway(grouped_test2.get_group('fwd')['price'], grouped_test2.get_group('rwd')['price'], grouped_test2.get_group('4wd')['price'])
 print( "ANOVA results: F=", f_val, ", P =", p_val)
# This is a great result, with a large F test score showing a strong correlation and a P value of almost 0 implying almost certain statistical significance.

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