Source:
import polars as pl
import numpy as np
from scipy.optimize import minimize
from scipy.special import gammaln, hyp2f1, gamma, factorial
from utils import CDNOW
import altair as alt
from IPython.display import display_markdown
alt.renderers.enable("html")RendererRegistry.enable('html')calib_p = 273 # 39 week calibration period
data = CDNOW(master=False, calib_p=calib_p)
rfm_data = data.rfm_summary()
# Time of trial purchase (in weeks)
tofp = data.time_to_trail_purch()
# actual weekly & cumulative repeat sales data
actual_repeat_sales = data.repeat_sales()
forecast_horizon_week = (calib_p * 2) // 7
forecast_horizon_day = forecast_horizon_week * 7
forecast_horizon_day
t = np.arange(forecast_horizon_day, dtype=np.int16) + 1
tofp_array = tofp.collect().to_numpy()
num_triers = tofp_array[:, 1]
trial_weeks = tofp_array[:, 0]
trial_days = np.arange(np.max(trial_weeks) * 7, dtype=np.int16) + 1def bgnbd_est(rfm_data, guess={"r": 0.01, "alpha": 0.01, "a": 0.01, "b": 0.01}):
def log_likelihood(x):
r, alpha, a, b = x
p1x, t_x, T = rfm_data[:, 0], rfm_data[:, 1], rfm_data[:, 2]
ln_A_1 = gammaln(p1x + r) - gammaln(r) + r * np.log(alpha)
ln_A_2 = gammaln(a + b) + gammaln(b + p1x) - gammaln(b) - gammaln(a + b + p1x)
ln_A_3 = -(r + p1x) * np.log(alpha + T)
ln_A_4 = np.where(
p1x > 0,
np.log(a) - np.log(b + p1x - 1) - (r + p1x) * np.log(alpha + t_x),
0,
)
return -np.sum(
ln_A_1 + ln_A_2 + np.log(np.exp(ln_A_3) + (p1x > 0) * np.exp(ln_A_4))
)
bnds = [(1e-6, np.inf) for _ in range(4)]
return minimize(
log_likelihood,
x0=list(guess.values()),
bounds=bnds,
method="Nelder-Mead",
options={"maxiter": 10000},
)result = bgnbd_est(rfm_data.select("P1X", "t_x", "T").collect().to_numpy())
r, alpha, a, b = result.x
ll = result.fun
# Sample Parameters
# r = 0.24259395230803
# alpha = 4.41359091416604
# a = 0.792919955839573
# b = 2.42589404751842
display_markdown(
f"""$r$ = {r:0.4f}
$\\alpha$ = {alpha:0.4f}
$a$ = {a:0.4f}
$b$ = {b:0.4f}
Log-Likelihood = {-ll:0.4f}""",
raw=True,
)/var/folders/0s/z9xp988n3j78zfjwg3y616x00000gn/T/ipykernel_19228/3229766705.py:11: RuntimeWarning:
invalid value encountered in log
\(r\) = 0.2426
\(\alpha\) = 4.4136
\(a\) = 0.7929
\(b\) = 2.4259
Log-Likelihood = -9582.4292
def bgnbd_est(rfm_data, guess={"r": 0.01, "alpha": 0.01, "a": 0.01, "b": 0.01}):
def log_likelihood(x):
r, alpha, a, b = x
p1x, t_x, T = (
rfm_data[:, 0],
rfm_data[:, 1] / 4,
rfm_data[:, 2] / 4,
) # change the unit of time in the above example from week to quad-week
ln_A_1 = gammaln(p1x + r) - gammaln(r) + r * np.log(alpha)
ln_A_2 = gammaln(a + b) + gammaln(b + p1x) - gammaln(b) - gammaln(a + b + p1x)
ln_A_3 = -(r + p1x) * np.log(alpha + T)
ln_A_4 = np.where(
p1x > 0,
np.log(a) - np.log(b + p1x - 1) - (r + p1x) * np.log(alpha + t_x),
0,
)
return -np.sum(
ln_A_1 + ln_A_2 + np.log(np.exp(ln_A_3) + (p1x > 0) * np.exp(ln_A_4))
)
bnds = [(1e-6, np.inf) for _ in range(4)]
return minimize(
log_likelihood,
x0=list(guess.values()),
bounds=bnds,
method="Nelder-Mead",
options={"maxiter": 10000},
)result = bgnbd_est(rfm_data.select("P1X", "t_x", "T").collect().to_numpy())
r, alpha, a, b = result.x
ll = result.fun
display_markdown(
f"""$r$ = {r:0.4f}
$\\alpha$ = {alpha:0.4f}
$a$ = {a:0.4f}
$b$ = {b:0.4f}
Log-Likelihood = {-ll:0.4f}""",
raw=True,
)/var/folders/0s/z9xp988n3j78zfjwg3y616x00000gn/T/ipykernel_19228/2910011743.py:15: RuntimeWarning:
invalid value encountered in log
\(r\) = 0.2426
\(\alpha\) = 1.1034
\(a\) = 0.7929
\(b\) = 2.4259
Log-Likelihood = -6176.3040
def bgnbd_est(rfm_data, guess={"r": 0.01, "alpha": 0.01, "a": 0.01, "b": 0.01}):
def log_likelihood(x):
r, alpha, a, b = x
p1x, t_x, T = rfm_data[:, 0], rfm_data[:, 1], rfm_data[:, 2]
D_1 = (
gammaln(r + p1x)
- gammaln(r)
+ gammaln(a + b)
+ gammaln(b + p1x)
- gammaln(b)
- gammaln(a + b + p1x)
)
D_2 = r * np.log(alpha, where=alpha > 0) - (r + p1x) * np.log(
alpha + t_x, where=((alpha > 0) or (t_x > 0))
)
C_3 = ((alpha + t_x) / (alpha + T)) ** (r + p1x)
C_4 = a / (b + p1x - 1)
return -np.sum(
D_1
+ D_2
+ np.where(p1x > 0, np.log(C_3 + C_4, where=(C_3 + C_4) > 0), np.log(C_3))
)
bnds = [(1e-6, np.inf) for _ in range(4)]
return minimize(
log_likelihood,
x0=list(guess.values()),
bounds=bnds,
method="Nelder-Mead",
options={"maxiter": 10000},
)result = bgnbd_est(rfm_data.select("P1X", "t_x", "T").collect().to_numpy())
r, alpha, a, b = result.x
ll = result.fun
display_markdown(
f"""$r$ = {r:0.4f}
$\\alpha$ = {alpha:0.4f}
$a$ = {a:0.4f}
$b$ = {b:0.4f}
Log-Likelihood = {-ll:0.4f}""",
raw=True,
)\(r\) = 0.2426
\(\alpha\) = 4.4136
\(a\) = 0.7929
\(b\) = 2.4259
Log-Likelihood = -9582.4292
def bgnbd_est(rfm_data, guess={"r": 0.01, "alpha": 0.01, "a": 0.01, "b": 0.01}):
def log_likelihood(x):
r, alpha, a, b = x
p1x, t_x, T = rfm_data[:, 0], rfm_data[:, 1], rfm_data[:, 2]
# Logarithm calculations with numerical stability
log_alpha = np.log(
np.clip(alpha, 1e-10, None)
) # Avoid log(0) by clipping to a small value
log_alpha_t_x = np.log(np.clip(alpha + t_x, 1e-10, None))
# Components of the log-likelihood
D_1 = (
gammaln(r + p1x)
- gammaln(r)
+ gammaln(a + b)
+ gammaln(b + p1x)
- gammaln(b)
- gammaln(a + b + p1x)
)
D_2 = r * log_alpha - (r + p1x) * log_alpha_t_x
C_3 = ((alpha + t_x) / (alpha + T)) ** (r + p1x)
C_4 = a / (b + p1x - 1)
# Handle cases where p1x > 0 and apply log to valid values
log_term = np.log(np.clip(C_3 + C_4, 1e-10, None))
result = (
D_1 + D_2 + np.where(p1x > 0, log_term, np.log(np.clip(C_3, 1e-10, None)))
)
return -np.sum(result)
# Bounds for the optimization
bnds = [(1e-6, np.inf) for _ in range(4)]
# Optimization using minimize
return minimize(
log_likelihood,
x0=list(guess.values()),
bounds=bnds,
method="Nelder-Mead",
options={"maxiter": 20000},
)result = bgnbd_est(rfm_data.select("P1X", "t_x", "T").collect().to_numpy())
r, alpha, a, b = result.x
ll = result.fun
display_markdown(
f"""$r$ = {r:0.4f}
$\\alpha$ = {alpha:0.4f}
$a$ = {a:0.4f}
$b$ = {b:0.4f}
Log-Likelihood = {-ll:0.4f}""",
raw=True,
)\(r\) = 0.2426
\(\alpha\) = 4.4136
\(a\) = 0.7929
\(b\) = 2.4259
Log-Likelihood = -9582.4292
z = (t / 7) / (alpha + (t / 7))
h2f1 = hyp2f1(r, b, (a + b - 1), z)
E_X_t = (a + b - 1) / (a - 1) * (1 - (alpha / (alpha + (t / 7))) ** r * h2f1)
index = t.reshape(-1, 1) - trial_days
index = np.clip(index - 1, 0, E_X_t.shape[0]).T
# Compute cumulative repeat sales
cum_rpt_sls = np.dot(num_triers, np.triu(E_X_t[index], k=1))[6::7]
# Compute weekly repeat sales
wkly_rpt_sls = np.diff(cum_rpt_sls, prepend=0)
bgnbd_repeat_sales = pl.DataFrame(
{
"Week": np.arange(cum_rpt_sls.shape[0]) + 1,
"Weekly Sales": wkly_rpt_sls,
"Cum Sales": cum_rpt_sls,
},
schema={"Week": pl.UInt16, "Weekly Sales": pl.Float32, "Cum Sales": pl.Float32},
)rfm_data_array = rfm_data.select("P1X", "P2X", "t_x", "T").collect().to_numpy()
p1x = rfm_data_array[:, 0].astype(np.int16)
p2x = rfm_data_array[:, 1].astype(np.int16)
t_x = rfm_data_array[:, 2]
T = rfm_data_array[:, 3]
t_ce = (
39 # the length of the period over which we wish to make the conditional forecast
)
h2f1_cust = hyp2f1(r + p1x, b + p1x, a + b + p1x - 1, t_ce / (alpha + T + t_ce))
ce = (
(a + b + p1x - 1)
/ (a - 1)
* (1 - ((alpha + T) / (alpha + T + t_ce)) ** (r + p1x) * h2f1_cust)
/ (1 + (p1x > 0) * a / (b + p1x - 1) * ((alpha + T) / (alpha + t_x)) ** (r + p1x))
)
individual_trans = pl.DataFrame({"Actual": p2x, "BG/NBD": ce})
# Compute unique levels of p1x
unique_p1x = np.arange(p1x.max() + 1)
# Compute counts per unique p1x
np1x = np.bincount(p1x)
ce_act = np.divide(np.bincount(p1x, weights=p2x), np1x, where=np1x != 0)
ce_est = np.divide(np.bincount(p1x, weights=ce), np1x, where=np1x != 0)
# create right-censored version for plot
censor = 7 # right-censor at 7+
denom = np.sum(np1x[censor:])
# Compute censored actual conditional expectations
ce_act_cen = np.zeros(censor + 1)
ce_act_cen[:censor] = ce_act[:censor]
ce_act_cen[censor] = np.dot(np1x[censor:], ce_act[censor:]) / denom
# Compute censored estimated conditional expectations
ce_est_cen = np.zeros(censor + 1)
ce_est_cen[:censor] = ce_est[:censor]
ce_est_cen[censor] = np.dot(np1x[censor:], ce_est[censor:]) / denom
ce_bgnbd = pl.DataFrame(
{
"P1X": [str(i) if i < 7 else "7+" for i in range(8)],
"Empirical": ce_act_cen,
"BG/NBD": ce_est_cen,
}
)p1x_cust = 2
t_x_cust = 30.43
T_cust = 38.86
t_ce = 39 # the length of the period over which we wish to make the conditional forecast
h2f1_cust = hyp2f1(
r + p1x_cust, b + p1x_cust, a + b + p1x_cust - 1, t_ce /
(alpha + T_cust + t_ce)
)
E_Y_X = (
(a + b + p1x_cust - 1) / (a - 1)
* (1 - ((alpha + T_cust) / (alpha + T_cust + t_ce)) ** (r + p1x_cust) * h2f1_cust)
/ (
1 + (p1x_cust > 0) * a / (b + p1x_cust - 1)
* ((alpha + T_cust) / (alpha + t_x_cust)) ** (r + p1x_cust)
)
)
display_markdown(
f"""$E(Y(t) \\mid X = x, t_{{x}}, T, r, \\alpha, a, b)$ = {E_Y_X:0.4f}""", raw=True
)\(E(Y(t) \mid X = x, t_{x}, T, r, \alpha, a, b)\) = 1.2259
T = 39 - trial_weeks # length of the period of time over which the customer could have made repeat purchases
B_a_b = np.exp(gammaln(a) + gammaln(b) - gammaln(a + b))
T_A, p1x_A = np.meshgrid(T, np.arange(5) + 1)
A = np.ones((T_A.shape[0] + 1, T_A.shape[1]))
A[1:, :] = (
np.exp(gammaln(r + p1x_A) - gammaln(r) - gammaln(p1x_A + 1))
* (T_A / (alpha + T_A)) ** p1x_A
)
A = np.cumsum(A, axis=0)
T_P_X_T, p1x_P_X_T = np.meshgrid(T, np.arange(6) + 1)
P_X_t = np.zeros((T_P_X_T.shape[0] + 2, T_P_X_T.shape[1]))
P_X_t[0] = (
np.exp(gammaln(a) + gammaln(b + 0) - gammaln(a + b + 0))
/ B_a_b
* np.exp(gammaln(r + 0) - gammaln(r) - gammaln(0 + 1))
* (alpha / (alpha + T)) ** r
* (T / (alpha + T)) ** 0
)
P_X_t[1:-1, :] = np.exp(
gammaln(a) + gammaln(b + p1x_P_X_T) - gammaln(a + b + p1x_P_X_T)
) / B_a_b * np.exp(gammaln(r + p1x_P_X_T) - gammaln(r) - gammaln(p1x_P_X_T + 1)) * (
alpha / (alpha + T_P_X_T)
) ** r * (T_P_X_T / (alpha + T_P_X_T)) ** p1x_P_X_T + np.exp(
gammaln(a + 1) + gammaln(b + p1x_P_X_T - 1) - gammaln(a + b + p1x_P_X_T)
) / B_a_b * (1 - (alpha / (alpha + T_P_X_T)) ** r * A)
P_X_t[-1] = 1 - np.sum(P_X_t[:-1], axis=0)
E_f_x = np.dot(P_X_t, num_triers)
bgnbd_hist = pl.Series('BG/NBD', E_f_x)fit_hist_bgnbd = (
rfm_data.with_columns(
pl.col("P1X").cut(
breaks=range(7), labels=[str(i) if i < 7 else "7+" for i in range(8)]
)
)
.group_by("P1X")
.agg(pl.len().alias("Actual"))
.sort("P1X")
.collect()
.hstack([bgnbd_hist])
.with_columns(
((pl.col("Actual") - pl.col("BG/NBD")) ** 2 / pl.col("BG/NBD")).alias(
"(O-E)^2/E - BG/NBD"
)
)
)
chi_square = fit_hist_bgnbd.select("(O-E)^2/E - BG/NBD").sum()
chi_square| (O-E)^2/E - BG/NBD |
|---|
| f64 |
| 4.821229 |
def paretonbd_est(rfm_data, guess={"r": 1, "alpha": 1, "s": 1, "beta": 1}):
def log_likelihood(x):
r, alpha, s, beta = x
p1x, t_x, T = rfm_data[:, 0], rfm_data[:, 1], rfm_data[:, 2]
maxab = np.max((alpha, beta))
absab = np.abs(alpha - beta)
param2 = s + 1
if alpha < beta:
param2 = r + p1x
part1 = (alpha**r * beta**s / gamma(r)) * gamma(r + p1x)
part2 = 1 / ((alpha + T) ** (r + p1x) * (beta + T) ** s)
if absab == 0:
F1 = 1 / ((maxab + t_x) ** (r + s + p1x))
F2 = 1 / ((maxab + T) ** (r + s + p1x))
else:
F1 = hyp2f1(r + s + p1x, param2, r + s + p1x + 1, absab / (maxab + t_x)) / (
(maxab + t_x) ** (r + s + p1x)
)
F2 = hyp2f1(r + s + p1x, param2, r + s + p1x + 1, absab / (maxab + T)) / (
(maxab + T) ** (r + s + p1x)
)
return -np.sum(np.log(part1 * (part2 + (s / (r + s + p1x)) * (F1 - F2))))
bnds = [(1e-6, 20) for _ in range(4)]
return minimize(
log_likelihood,
x0=list(guess.values()),
bounds=bnds,
method="Nelder-Mead",
options={"maxiter": 10000},
)result = paretonbd_est(rfm_data.select("P1X", "t_x", "T").collect().to_numpy())
r, alpha, s, beta = result.x
ll = result.fun
# Sample Parameters
# r = 0.553268332737686
# alpha = 10.577643207793674
# s = 0.606338658139013
# beta = 11.672047422351444
display_markdown(
f"""$r$ = {r:0.4f}
$\\alpha$ = {alpha:0.4f}
$s$ = {a:0.4f}
$\\beta$ = {b:0.4f}
Log-Likelihood = {-ll:0.4f}""",
raw=True,
)\(r\) = 0.5533
\(\alpha\) = 10.5777
\(s\) = 0.7929
\(\beta\) = 2.4259
Log-Likelihood = -9594.9762
E_X_t = r * beta / (alpha * (s - 1)) * (1 - (beta / (beta + (t / 7))) ** (s - 1))
index = t.reshape(-1, 1) - trial_days
index = np.clip(index - 1, 0, E_X_t.shape[0]).T
# Compute cumulative repeat sales
cum_rpt_sls = np.dot(num_triers, np.triu(E_X_t[index], k=1))[6::7]
# Compute weekly repeat sales
wkly_rpt_sls = np.diff(cum_rpt_sls, prepend=0)
paretonbd_repeat_sales = pl.DataFrame(
{
"Week": np.arange(cum_rpt_sls.shape[0]) + 1,
"Weekly Sales": wkly_rpt_sls,
"Cum Sales": cum_rpt_sls,
},
schema={"Week": pl.UInt16, "Weekly Sales": pl.Float32, "Cum Sales": pl.Float32},
)cum_sales_plot_data = (
actual_repeat_sales.rename({"Cum Sales": "Actual"})
.join(other=paretonbd_repeat_sales, on="Week", how="left", suffix=" - Pareto/NBD")
.rename({"Cum Sales": "Pareto/NBD"})
.join(other=bgnbd_repeat_sales, on="Week", how="left", suffix=" - BG/NBD")
.rename({"Cum Sales": "BG/NBD"})
.unpivot(
on=["Actual", "Pareto/NBD", "BG/NBD"],
index="Week",
value_name="Cum Sales",
variable_name="Actual Vs Estimated",
)
)
(
alt.Chart(cum_sales_plot_data)
.mark_line()
.encode(
x=alt.X("Week", title="Week"),
y=alt.Y("Cum Sales", title="Cum. Rpt Transactions"),
strokeDash="Actual Vs Estimated:N",
)
.properties(width=550, height=400, title="Tracking Cumulative Repeat Transactions")
.configure_view(stroke=None)
.configure_axisY(grid=False)
.configure_axisX(grid=False)
)weekly_sales_plot_data = (
actual_repeat_sales.rename({"Weekly Sales": "Actual"})
.join(other=paretonbd_repeat_sales, on="Week", how="left", suffix=" - Pareto/NBD")
.rename({"Weekly Sales": "Pareto/NBD"})
.join(other=bgnbd_repeat_sales, on="Week", how="left", suffix=" - BG/NBD")
.rename({"Weekly Sales": "BG/NBD"})
.unpivot(
on=["Actual", "Pareto/NBD", "BG/NBD"],
index="Week",
value_name="Weekly Sales",
variable_name="Actual Vs Estimated",
)
)
(
alt.Chart(weekly_sales_plot_data)
.mark_line()
.encode(
x=alt.X("Week", title="Week"),
y=alt.Y("Weekly Sales", title="Weekly Rpt Transactions"),
strokeDash="Actual Vs Estimated:N",
)
.properties(width=650, height=250, title="Tracking Weekly Repeat Transactions")
.configure_view(stroke=None)
.configure_axisY(grid=False)
.configure_axisX(grid=False)
)# Compute P(active|p1x,tx,T)
rfm_data_array = rfm_data.select("P1X", "P2X", "t_x", "T").collect().to_numpy()
p1x = rfm_data_array[:, 0].astype(np.int16)
p2x = rfm_data_array[:, 1].astype(np.int16)
t_x = rfm_data_array[:, 2]
T = rfm_data_array[:, 3]
maxab = np.max((alpha, beta))
absab = np.abs(alpha - beta)
param2 = s + 1
if alpha < beta:
param2 = r + p1x
F0 = (alpha + T) ** (r + p1x) * (beta + T) ** s
if absab == 0:
F1 = 1 / ((maxab + t_x) ** (r + s + p1x))
F2 = 1 / ((maxab + T) ** (r + s + p1x))
else:
F1 = hyp2f1(r + s + p1x, param2, r + s + p1x + 1, absab / (maxab + t_x)) / (
(maxab + t_x) ** (r + s + p1x)
)
F2 = hyp2f1(r + s + p1x, param2, r + s + p1x + 1, absab / (maxab + T)) / (
(maxab + T) ** (r + s + p1x)
)
pactive = 1 / (1 + (s / (r + s + p1x)) * F0 * (F1 - F2))
# compute average P(active|p1x,tx,T) and determine the proportion of customers buying in the second 39 weeks for each level of p1x
# Compute unique levels of p1x
unique_p1x = np.arange(p1x.max() + 1)
# Compute counts per unique p1x
np1x = np.bincount(p1x)
# Compute actual proportions of active customers
pa_actual = np.divide(
np.bincount(p1x, weights=(p2x > 0).astype(float)), np1x, where=np1x != 0
)
# Compute estimated proportions of active customers
pa_est = np.divide(np.bincount(p1x, weights=pactive), np1x, where=np1x != 0)# create right-censored version for plot
censor = 7 # Right-censor at 7+
denom = np.sum(np1x[censor:]) # Compute denominator
# Compute censored actual proportions
pa_act_cen = np.zeros(censor + 1)
pa_act_cen[:censor] = pa_actual[:censor]
pa_act_cen[censor] = np.dot(np1x[censor:], pa_actual[censor:]) / denom
# Compute censored estimated proportions
pa_est_cen = np.zeros(censor + 1)
pa_est_cen[:censor] = pa_est[:censor]
pa_est_cen[censor] = np.dot(np1x[censor:], pa_est[censor:]) / denom
prop_active_customers = pl.DataFrame(
{
"P1X": [str(i) if i < 7 else "7+" for i in range(8)],
"Empirical": pa_act_cen,
"Pareto/NBD": pa_est_cen,
}
)
prop_active_customers = prop_active_customers.unpivot(
on=["Empirical", "Pareto/NBD"],
index="P1X",
variable_name="Actual Vs Estimated",
value_name="P(active)",
)
(
alt.Chart(prop_active_customers)
.mark_line()
.encode(
x=alt.X(
"P1X:O", title="# Transactions in Weeks 1−39", axis=alt.Axis(labelAngle=0)
),
y=alt.Y("P(active):Q", title="P(Active)"),
strokeDash="Actual Vs Estimated:N",
)
.properties(
width=550,
height=400,
title="Predicted vs. Actual Proportions of Active Customers",
)
.configure_view(stroke=None)
.configure_axisY(grid=False)
.configure_axisX(grid=False)
)t_ce = 39 # period for which conditional expectations are to be computed
tmp1 = (r + p1x) * (beta + T) / ((alpha + T) * (s - 1))
tmp2 = ((beta + T) / (beta + T + t_ce)) ** (s - 1)
ce = tmp1 * (1 - tmp2) * pactive
individual_trans = individual_trans.hstack([pl.Series("Pareto/NBD", ce)])
# compute average E[Y(t)|p1x,tx,T] and average actual number of
# transactions in the second 39 weeks for each level of p1x
# Compute unique levels of p1x
unique_p1x = np.arange(p1x.max() + 1)
# Compute counts per unique p1x
np1x = np.bincount(p1x)
ce_est = np.divide(np.bincount(p1x, weights=ce), np1x, where=np1x != 0)# create right-censored version for plot
censor = 7 # right-censor at 7+
denom = np.sum(np1x[censor:])
# Compute censored estimated conditional expectations
ce_est_cen = np.zeros(censor + 1)
ce_est_cen[:censor] = ce_est[:censor]
ce_est_cen[censor] = np.dot(np1x[censor:], ce_est[censor:]) / denom
conditional_expectation = ce_bgnbd.hstack([pl.Series("Pareto/NBD", ce_est_cen)])
conditional_expectation = conditional_expectation.unpivot(
on=["Empirical", "BG/NBD", "Pareto/NBD"],
index="P1X",
variable_name="Actual Vs Estimated",
value_name="CE P2X",
)(
alt.Chart(conditional_expectation)
.mark_line()
.encode(
x=alt.X(
"P1X:O", title="# Transactions in Weeks 1−39", axis=alt.Axis(labelAngle=0)
),
y=alt.Y("CE P2X:Q", title="Average # Transactions in Weeks 40−78"),
strokeDash=alt.StrokeDash(
"Actual Vs Estimated:N",
scale=alt.Scale(domain=["Empirical", "BG/NBD", "Pareto/NBD"]),
),
)
.properties(
width=550,
height=400,
title="Conditional Expectations of Purchasing (Weeks 40–78)",
)
.configure_view(stroke=None)
.configure_axisY(grid=False)
.configure_axisX(grid=False)
)T = 39 - trial_weeks # length of the period of time over which the customer could have made repeat purchases
T_P_X_T, p1x_P_X_T = np.meshgrid(T, np.arange(7))
maxab = np.max((alpha, beta))
absab = np.abs(alpha - beta)
param2 = s + 1
if alpha < beta:
param2 = r + p1x_P_X_T
B2i = hyp2f1(
r + s + p1x_P_X_T, param2, r + s + p1x_P_X_T + 1, absab / (maxab + T_P_X_T)
) / ((maxab + T_P_X_T) ** (r + s + p1x_P_X_T))
A = (
np.exp(gammaln(r + s + p1x_P_X_T) - gammaln(r + s))
* T_P_X_T**p1x_P_X_T
/ factorial(p1x_P_X_T, exact=True)
* B2i
)
A = np.cumsum(A, axis=0)
B1 = hyp2f1(r + s, param2, r + s + p1x_P_X_T + 1, absab / maxab) / (maxab ** (r + s))
B_r_s = np.exp(gammaln(r) + gammaln(s) - gammaln(r + s))
P_X_t = np.zeros((T_P_X_T.shape[0] + 1, T_P_X_T.shape[1]))
P_X_t[:-1] = np.exp(gammaln(r + p1x_P_X_T) - gammaln(r) - gammaln(p1x_P_X_T + 1)) * (
alpha / (alpha + T_P_X_T)
) ** r * (T_P_X_T / (alpha + T_P_X_T)) ** p1x_P_X_T * (
beta / (beta + T_P_X_T)
) ** s + alpha**r * beta**s * np.exp(
gammaln(r + p1x_P_X_T) + gammaln(s + 1) - gammaln(r + p1x_P_X_T + s + 1)
) / B_r_s * (B1 - A)
P_X_t[-1] = 1 - np.sum(P_X_t[:-1], axis=0)
E_f_x = np.dot(P_X_t, num_triers)
paretonbd_hist = pl.Series("Pareto/NBD", E_f_x)fit_hist = fit_hist_bgnbd.hstack([paretonbd_hist]).with_columns(
((pl.col("Actual") - pl.col("Pareto/NBD")) ** 2 / pl.col("Pareto/NBD")).alias(
"(O-E)^2/E - Pareto/NBD"
)
)
chi_square_paretonbd = fit_hist.select("(O-E)^2/E - Pareto/NBD").sum()
chi_square_paretonbd| (O-E)^2/E - Pareto/NBD |
|---|
| f64 |
| 11.561473 |
barchart_data = fit_hist.unpivot(
on=["Actual", "BG/NBD", "Pareto/NBD"],
index="P1X",
variable_name="Actual Vs Estimated",
value_name="Frequency",
)
(
alt.Chart(barchart_data)
.mark_bar()
.encode(
x=alt.X(
"P1X:O", title="# Transactions in Weeks 1−39", axis=alt.Axis(labelAngle=0)
),
y=alt.Y("Frequency:Q", title="Frequency"),
color="Actual Vs Estimated:N",
# column='Actual Vs Estimated:N',
xOffset="Actual Vs Estimated:N",
)
.properties(
width=550,
height=400,
title="Predicted Versus Actual Frequency of Repeat Transactions",
)
.configure_view(stroke=None)
.configure_axisY(grid=False)
.configure_axisX(grid=False)
)(
individual_trans.corr()
.with_columns(pl.Series(individual_trans.columns).alias("index"))
.style.tab_header(title="Correlations Between Forecast Period Transaction Numbers")
.tab_stub(rowname_col="index")
.fmt_number(decimals=3)
)| Correlations Between Forecast Period Transaction Numbers | |||
|---|---|---|---|
| Actual | BG/NBD | Pareto/NBD | |
| Actual | 1.000 | 0.626 | 0.630 |
| BG/NBD | 0.626 | 1.000 | 0.996 |
| Pareto/NBD | 0.630 | 0.996 | 1.000 |