1 EVOLUCIÓN DE LAS VENTAS NETAS

  • Hemos escogido para este estudio un extracto de datos referente a la “Evolucion mensual de las Ventas Netas de Estilos S.R.L, en el periodo entre el 1 Enero del 2019 y 15 Febrero del 2023. Fuente: Cubo Empresa al 15 de febrero del 2023

  • De este mismo extracto vamos a pronosticar las ventas netas de los siguientes 100 dias.

  • Una vez hecha las predicciones y comparados todos los modelos con los resultados reales, procederemos a estimar el error de cada modelo, para posteriormente elegir el mejor o los mejores modelos de pronostico de todos los que hemos representado.

2 MODELO ARIMA

  • Un modelo autorregresivo integrado de promedio movil o ARIMA es un modelo estadistico que utiliza variaciones y regresiones de datos estadisticos con el fin de encontrar patrones para una prediccion hacia el futuro. Se trata de un modelo dinamico de series temporales, es decir, las estimaciones futuras vienen explicadas por los datos del pasado y no por variables independientes.

3 CUESTIONES IMPORTANTES A TENER EN CUENTA

  • Para definir un modelo ARIMA, debemos tener en cuenta que los datos deben ser estacionarios,es decir cuando su distribucion y sus parametros no varian con el tiempo.

  • Otra cuestion para tener en cuenta es que los datos deben ser univariantes, ARIMA trabaja en una sola variable.

  • La regresion automatica tiene que ver con los valores pasados, es decir necesitamos un historico de los datos para poder realizar el modelo y asi predecir datos futuros.

4 PROCESO DEL MODELO

  • Comenzamos cargando las librerias previamente instaladas, que nos hacen falta para ejecutar el modelo tal como “tidyverse” para realizar transformaciones en general de nuestro conjunto de datos, ademas de otras funciones asociadas ,“readxl” para leer los datos de un archivo excel, “lubridate” para hacer transformaciones en un campo fecha, y forecast que es una libreria empleada para pronosticos de series de tiempo
library(forecast) 
## Registered S3 method overwritten by 'quantmod':
##   method            from
##   as.zoo.data.frame zoo
library(openxlsx)
library(tidyverse)
## ── Attaching packages ─────────────────────────────────────── tidyverse 1.3.2
## ──
## ✔ ggplot2 3.4.1     ✔ purrr   1.0.1
## ✔ tibble  3.1.8     ✔ dplyr   1.1.0
## ✔ tidyr   1.3.0     ✔ stringr 1.5.0
## ✔ readr   2.1.4     ✔ forcats 1.0.0
## ── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──
## ✖ dplyr::filter() masks stats::filter()
## ✖ dplyr::lag()    masks stats::lag()
library(readxl)
library(lubridate)
## 
## Attaching package: 'lubridate'
## 
## The following objects are masked from 'package:base':
## 
##     date, intersect, setdiff, union
library(tseries)
library(ggplot2)
library(astsa)
## 
## Attaching package: 'astsa'
## 
## The following object is masked from 'package:forecast':
## 
##     gas

A continuación vamos a cargar nuestros conjunto de datos del archivo excel que los contiene:

Pronostico_2019_2023 <- read_excel("C:/Users/lzavalaga/Desktop/Pronostico  2019-2023.xlsx")
Pronostico_2019_2023
  • Ahora vamos a hacer las transformaciones dentro del dataset en el campo “Fecha” correspondientes para separar mes, año y luego añadir la variable objetivo de pronostico “Venta Neta”, para configurar nuestro conjunto de datos del cual vamos a partir para iniciar nuestro pronostico, todo ello guardado en la variable STventas, donde mostramos los resultados de la transformación
Pronostico_2019_2023 %>%
  
  mutate_at(vars(Fecha), list(year=year, month=month, day=day))%>%
  select("Venta Neta")-> STventas

STventas

Ahora es necesario convertir nuestro dataset en una serie de tiempo

Ventas<-ts(STventas, start = c(2019,1,1),frequency = 365)
Ventas
## Time Series:
## Start = c(2019, 1) 
## End = c(2023, 43) 
## Frequency = 365 
##         Venta Neta
##    [1,]      25.38
##    [2,]  755835.71
##    [3,]  554626.22
##    [4,]  621512.79
##    [5,]  789422.43
##    [6,]  685766.56
##    [7,]  491707.54
##    [8,]  592440.12
##    [9,]  660975.84
##   [10,]  570738.38
##   [11,]  609650.57
##   [12,]  793634.88
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##   [15,]  538001.79
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##   [19,]  843583.59
##   [20,]  674093.31
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## [1442,] 1082212.28
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## [1449,] 2863770.06
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## [1452,] 1058423.18
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## [1454,]  821616.69
## [1455,] 1024040.23
## [1456,] 1422091.06
## [1457,] 1838921.52
## [1458,]    6275.55
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## [1467,]  521990.46
## [1468,]  470785.76
## [1469,]  379898.07
## [1470,]  544701.16
## [1471,]  720741.35
## [1472,]  652290.73
## [1473,]  604720.69
## [1474,]  496968.71
## [1475,]  511103.26
## [1476,]  311580.49
## [1477,]  482448.13
## [1478,]  725868.82
## [1479,]  602534.74
## [1480,]  562300.35
## [1481,]  592590.18
## [1482,]  481878.53
## [1483,]  548663.77
## [1484,]  611216.88
## [1485,]  711802.21
## [1486,]  621027.34
## [1487,]  512292.10
## [1488,]  594959.78
## [1489,]  474381.73
## [1490,]  510496.15
## [1491,]  673021.03
## [1492,]  963059.43
## [1493,]  627395.31
## [1494,]  594324.70
## [1495,]  651107.89
## [1496,]  608331.53
## [1497,]  677134.99
## [1498,]  548706.93
## [1499,]  936610.25
## [1500,]  878128.34
## [1501,]  593876.65
## [1502,]  555956.03
## [1503,]  602964.26
plot(Ventas)

Luego vamos a descomponer nuestra serie temporal

descomp = decompose(Ventas)
autoplot(descomp)

 En “data” podemos apreciar la grafica de los datos, en “seasonal” que es la estacionalidad, apreciamos el patron de los datos que se repite cada año, que es el patron que se mantiene constante.

 Por otro lado “trend” representa la tendencia, que es como se puede ver tiene primero una pequeña subida luego baja y luego a partir de ese punto toma una tendencia ascendente, y “remainder”, representa la configuracion de los residuos que va dejando el modelo, cuando disminuyen y cuando aumentan. Si sumamos las graficas de seasonal, trend y remainder nos da la grafica total data de la serie temporal
  • Vamos a comprobar ahora para asegurarnos si nuestra serie temporal es estacionaria o no a traves del test de Dickey-Fuller, si cumple en su ejecucion que el p-valor>0.05 la serie cumple la hipotesis nula en la cual la serie no es estacionaria, si por el contrario el p-valor<0.05 no se cumple la hipotesis nula con lo cual la serie es estacionaria, Asi pues lo comprobamos:
adf.test(Ventas)
## Warning in adf.test(Ventas): p-value smaller than printed p-value
## 
##  Augmented Dickey-Fuller Test
## 
## data:  Ventas
## Dickey-Fuller = -6.1955, Lag order = 11, p-value = 0.01
## alternative hypothesis: stationary
Y vemos que el p-valor nos sale 0.01<0.05 por tanto se rechaza la hipotesis nula y la serie es estacionaria. Cabe destacar que se recomienda siempre realizar una diferenciacion para poder decir con mas certeza que nuestros parametros no variaN en el tiempo.
  • Ahora vamos a utilizar 2 parametros “acf” y “pacf” que miden el nivel de residuos, de forma que los podemos ver graficamente. En la grafica aparece el nivel de los residuos y los rezagos(Lags), para identificar la serie de tiempo que sea autoregresiva los valores no deberian sobrepasar el nivel de significancia establecido representado por las lineas de rayas horizontales entrecortadas, como podemos ver los niveles de significancia.
Acf(Ventas)

pacf(Ventas)

Vamos a ver con el comando ndiffs(), que diferencias hay para poder arreglar nuestra serie temporal y poder convertirla a estacionaria y asi poder aplicar el modelo ARIMA.

ndiffs(Ventas)
## [1] 1

El comando ndiffs nos indica que hay una diferencia, que tenemos que arreglar, vamos a determinar la grafica que nos da cuando aplicamos la diferencia en el tiempo a la serie.

DSventas <- diff(Ventas, lag = 1)

plot(DSventas, main="Ventas Neta Estilos", xlab="Dias",ylab="Ventas")

autoplot(DSventas) +
  ggtitle("Ventas Neta Estilos") +
  ylab("ventas")

Si aplicamos ahora el test de Dickey-Fuller despues de la diferenciacion nos confirma y nos da un resultado < 0.05 lo que confirma que la serie ahora si es estacionaria.

adf.test(DSventas)
## Warning in adf.test(DSventas): p-value smaller than printed p-value
## 
##  Augmented Dickey-Fuller Test
## 
## data:  DSventas
## Dickey-Fuller = -13.852, Lag order = 11, p-value = 0.01
## alternative hypothesis: stationary

-Pasamos a continuacion a elaborar el modelo de pronostico ARIMA, con la funcion auto.arima. la funcion auto.arima esta diseñada para una estimacion rapida del modelo ARIMA probando varias series de tiempo.

-La funcion auto.arima, realiza la funcion ARIMA de forma automatica, va a ir iterando, va a ir buscando el modelo que mas se ajusta a los datos, y nos da respuesta del mejor modelo, como puede verse al ejecutar el print del mismo. El resultado despues de sucesivas iteraciones, se queda con el modelo que tuvo el menor valor de AIC.

#Modelo Arima con : Autorima

model <- auto.arima(Ventas, stepwise = T, approximation =T, seasonal=T,trace = T)
## 
##  Fitting models using approximations to speed things up...
## 
##  ARIMA(2,1,2)(1,0,1)[365] with drift         : Inf
##  ARIMA(0,1,0)             with drift         : 41990.12
##  ARIMA(1,1,0)(1,0,0)[365] with drift         : Inf
##  ARIMA(0,1,1)(0,0,1)[365] with drift         : Inf
##  ARIMA(0,1,0)                                : 41988.11
##  ARIMA(0,1,0)(1,0,0)[365] with drift         : Inf
##  ARIMA(0,1,0)(0,0,1)[365] with drift         : Inf
##  ARIMA(0,1,0)(1,0,1)[365] with drift         : Inf
##  ARIMA(1,1,0)             with drift         : 41832.63
##  ARIMA(1,1,0)(0,0,1)[365] with drift         : Inf
##  ARIMA(1,1,0)(1,0,1)[365] with drift         : Inf
##  ARIMA(2,1,0)             with drift         : 41792.53
##  ARIMA(2,1,0)(1,0,0)[365] with drift         : Inf
##  ARIMA(2,1,0)(0,0,1)[365] with drift         : Inf
##  ARIMA(2,1,0)(1,0,1)[365] with drift         : Inf
##  ARIMA(3,1,0)             with drift         : 41753.83
##  ARIMA(3,1,0)(1,0,0)[365] with drift         : Inf
##  ARIMA(3,1,0)(0,0,1)[365] with drift         : Inf
##  ARIMA(3,1,0)(1,0,1)[365] with drift         : Inf
##  ARIMA(4,1,0)             with drift         : 41705.17
##  ARIMA(4,1,0)(1,0,0)[365] with drift         : Inf
##  ARIMA(4,1,0)(0,0,1)[365] with drift         : Inf
##  ARIMA(4,1,0)(1,0,1)[365] with drift         : Inf
##  ARIMA(5,1,0)             with drift         : 41637.24
##  ARIMA(5,1,0)(1,0,0)[365] with drift         : Inf
##  ARIMA(5,1,0)(0,0,1)[365] with drift         : Inf
##  ARIMA(5,1,0)(1,0,1)[365] with drift         : Inf
##  ARIMA(5,1,1)             with drift         : 41576.97
##  ARIMA(5,1,1)(1,0,0)[365] with drift         : Inf
##  ARIMA(5,1,1)(0,0,1)[365] with drift         : Inf
##  ARIMA(5,1,1)(1,0,1)[365] with drift         : Inf
##  ARIMA(4,1,1)             with drift         : 41616.22
##  ARIMA(5,1,2)             with drift         : 41440.29
##  ARIMA(5,1,2)(1,0,0)[365] with drift         : Inf
##  ARIMA(5,1,2)(0,0,1)[365] with drift         : Inf
##  ARIMA(5,1,2)(1,0,1)[365] with drift         : Inf
##  ARIMA(4,1,2)             with drift         : 41574.1
##  ARIMA(5,1,3)             with drift         : 41410.93
##  ARIMA(5,1,3)(1,0,0)[365] with drift         : Inf
##  ARIMA(5,1,3)(0,0,1)[365] with drift         : Inf
##  ARIMA(5,1,3)(1,0,1)[365] with drift         : Inf
##  ARIMA(4,1,3)             with drift         : 41502.08
##  ARIMA(5,1,4)             with drift         : 41326.19
##  ARIMA(5,1,4)(1,0,0)[365] with drift         : Inf
##  ARIMA(5,1,4)(0,0,1)[365] with drift         : Inf
##  ARIMA(5,1,4)(1,0,1)[365] with drift         : Inf
##  ARIMA(4,1,4)             with drift         : Inf
##  ARIMA(5,1,5)             with drift         : 41317.11
##  ARIMA(5,1,5)(1,0,0)[365] with drift         : Inf
##  ARIMA(5,1,5)(0,0,1)[365] with drift         : Inf
##  ARIMA(5,1,5)(1,0,1)[365] with drift         : Inf
##  ARIMA(4,1,5)             with drift         : 41405.8
##  ARIMA(5,1,5)                                : 41315.08
##  ARIMA(5,1,5)(1,0,0)[365]                    : Inf
##  ARIMA(5,1,5)(0,0,1)[365]                    : Inf
##  ARIMA(5,1,5)(1,0,1)[365]                    : Inf
##  ARIMA(4,1,5)                                : 41403.77
##  ARIMA(5,1,4)                                : 41324.16
##  ARIMA(4,1,4)                                : Inf
## 
##  Now re-fitting the best model(s) without approximations...
## 
##  ARIMA(5,1,5)                                : 41345.48
## 
##  Best model: ARIMA(5,1,5)
print(model)
## Series: Ventas 
## ARIMA(5,1,5) 
## 
## Coefficients:
##          ar1      ar2     ar3      ar4      ar5      ma1     ma2      ma3
##       0.3525  -1.0342  0.1706  -0.5839  -0.3714  -0.8816  1.2406  -0.8301
## s.e.  0.0956   0.0921  0.1356   0.0844   0.0708   0.1002  0.1399   0.1704
##          ma4      ma5
##       0.7220  -0.1489
## s.e.  0.1344   0.0682
## 
## sigma^2 = 5.226e+10:  log likelihood = -20661.65
## AIC=41345.3   AICc=41345.48   BIC=41403.76

Ahra revisamos los resultados para los residuos

checkresiduals(model)

## 
##  Ljung-Box test
## 
## data:  Residuals from ARIMA(5,1,5)
## Q* = 1903.1, df = 291, p-value < 2.2e-16
## 
## Model df: 10.   Total lags used: 301
error=residuals(model)
plot(error)

tsdiag(model)

Ahora vamos a realizar un forecast para 100 días en el futuro

mod1 <- forecast(model, 100, level = 95)
autoplot(forecast(model, 100))

checkresiduals(model)

## 
##  Ljung-Box test
## 
## data:  Residuals from ARIMA(5,1,5)
## Q* = 1903.1, df = 291, p-value < 2.2e-16
## 
## Model df: 10.   Total lags used: 301
plot(mod1)

# Revisamos los pronosticos para los 100 dias
mod1
##           Point Forecast        Lo 95   Hi 95
## 2023.1178       553947.7   105902.262 1001993
## 2023.1205       653501.6   158276.562 1148727
## 2023.1233       796706.6   254869.593 1338544
## 2023.1260       745758.4   177057.050 1314460
## 2023.1288       607146.0    14058.911 1200233
## 2023.1315       595487.5   -10093.405 1201068
## 2023.1342       605449.8   -27916.807 1238816
## 2023.1370       573935.3  -118070.383 1265941
## 2023.1397       650389.2   -88343.374 1389122
## 2023.1425       769910.1     6066.409 1533754
## 2023.1452       726106.1   -60671.038 1512883
## 2023.1479       614806.9  -190496.960 1420111
## 2023.1507       608334.4  -208687.802 1425357
## 2023.1534       615504.0  -222745.067 1453753
## 2023.1562       586926.0  -291990.885 1465843
## 2023.1589       649587.1  -263169.247 1562343
## 2023.1616       747562.1  -185774.154 1680898
## 2023.1644       710633.9  -242290.083 1663558
## 2023.1671       621009.5  -348396.455 1590416
## 2023.1699       618352.7  -362441.355 1599147
## 2023.1726       623327.1  -375646.714 1622301
## 2023.1753       597714.1  -432609.082 1628037
## 2023.1781       649132.6  -407994.122 1706259
## 2023.1808       729427.0  -345625.781 1804480
## 2023.1836       698264.4  -394317.644 1790847
## 2023.1863       626122.9  -481658.966 1733905
## 2023.1890       626112.1  -492904.769 1745129
## 2023.1918       629421.0  -505881.941 1764724
## 2023.1945       606666.9  -554239.343 1767573
## 2023.1973       648917.7  -534329.196 1832165
## 2023.2000       714702.8  -484676.371 1914082
## 2023.2027       688384.7  -527051.564 1903821
## 2023.2055       630341.0  -599349.594 1860032
## 2023.2082       632104.7  -608695.822 1872905
## 2023.2110       634162.2  -621587.217 1889912
## 2023.2137       614096.9  -663370.189 1891564
## 2023.2164       648861.8  -647878.794 1945602
## 2023.2192       702742.7  -608810.781 2014296
## 2023.2219       680501.0  -645965.865 2006968
## 2023.2247       633822.6  -706135.399 1973781
## 2023.2274       636717.8  -714212.005 1987648
## 2023.2301       637846.6  -727012.050 2002705
## 2023.2329       620263.4  -763529.636 2004056
## 2023.2356       648906.9  -751938.004 2049752
## 2023.2384       693023.5  -721608.927 2107656
## 2023.2411       674216.4  -754395.513 2102828
## 2023.2438       636697.7  -804756.522 2078152
## 2023.2466       640255.9  -812009.767 2092522
## 2023.2493       640706.1  -824669.303 2106081
## 2023.2521       625381.6  -856852.365 2107615
## 2023.2548       649012.5  -848601.583 2146627
## 2023.2575       685122.0  -825451.029 2195695
## 2023.2603       669211.9  -854553.266 2192977
## 2023.2630       639073.1  -896966.056 2175112
## 2023.2658       642958.2  -903711.102 2189627
## 2023.2685       642922.5  -916174.720 2202020
## 2023.2712       629629.8  -944729.300 2203989
## 2023.2740       649150.2  -939292.863 2237593
## 2023.2767       678695.4  -922017.486 2279408
## 2023.2795       665231.5  -947995.692 2278459
## 2023.2822       641036.4  -983957.791 2266031
## 2023.2849       645012.1  -990414.526 2280439
## 2023.2877       644638.2 -1002634.040 2291910
## 2023.2904       633156.1 -1028119.063 2294431
## 2023.2932       649301.1 -1025028.170 2323630
## 2023.2959       673466.2 -1012546.728 2359479
## 2023.2986       662069.5 -1035865.300 2360004
## 2023.3014       642659.4 -1066584.897 2351904
## 2023.3041       646564.4 -1072903.600 2366032
## 2023.3068       645964.5 -1084842.115 2376771
## 2023.3096       636083.3 -1107712.750 2379879
## 2023.3123       649452.7 -1106561.890 2405467
## 2023.3151       669209.5 -1097981.257 2436400
## 2023.3178       659561.1 -1119028.136 2438150
## 2023.3205       644001.6 -1145481.348 2433485
## 2023.3233       647729.8 -1151761.532 2447221
## 2023.3260       646988.4 -1163393.668 2457370
## 2023.3288       638513.3 -1184027.553 2461054
## 2023.3315       649597.0 -1184471.758 2483666
## 2023.3342       665743.1 -1179056.412 2510543
## 2023.3370       657574.0 -1198157.460 2513305
## 2023.3397       645111.6 -1221133.653 2511357
## 2023.3425       648597.9 -1227438.049 2524634
## 2023.3452       647777.7 -1238748.668 2534304
## 2023.3479       640530.6 -1257462.945 2538524
## 2023.3507       649729.6 -1259211.764 2558671
## 2023.3534       662919.2 -1256357.356 2582196
## 2023.3562       656002.4 -1273787.413 2585792
## 2023.3589       646029.8 -1293925.370 2585985
## 2023.3616       649238.4 -1300290.359 2598767
## 2023.3644       648385.4 -1311272.806 2608044
## 2023.3671       642205.4 -1328335.909 2612747
## 2023.3699       649848.3 -1331146.448 2630843
## 2023.3726       660617.7 -1330357.336 2651593
## 2023.3753       654761.6 -1346348.936 2655872
## 2023.3781       646789.2 -1364165.873 2657744
## 2023.3808       649705.4 -1370609.252 2670020
## 2023.3836       648852.6 -1381263.591 2678969
## 2023.3863       643595.9 -1396903.859 2684096
## 2023.3890       649952.2 -1400573.929 2700478

5 CONCLUSIONES

  • El modelo Arima no logra capturar la tendencia diaria, lo cual no nos permite tener un mejor modelo(BIC)
  • El Modelo que logra mejor precision es el ARIMA(5,1,5)
  • El Modelo no cumple a cabalidad con un supuesto ya que los residuos tienen correlacion y el modelo no ha captado información
  • Se recomienda realizar el modelaje Arima para series mensuales y anuales con data mayor a 75 datos.