#Munkhzul Final
library(tidyquant) 
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library(lubridate)
library(timetk)
library(purrr)
library(quantmod)
library(dplyr)
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library(tidyr)

symbols <- c("SPY", "QQQ", "EEM", "IWM", "EFA", "TLT", "IYR", "GLD")

prices <- getSymbols(symbols, src = 'yahoo', from = "2010-01-01", auto.assign = TRUE, warnings = FALSE) %>% 
  map(~ Ad(get(.))) %>% 
  reduce(merge) %>%
  `colnames<-`(symbols)

prices_tibble <- tk_tbl(prices, rename_index = "date")

prices_tibble <- prices_tibble %>%
  mutate(date = as.character(date)) %>%
  mutate(date = as.Date(date))

weekly_prices <- prices_tibble %>%
  group_by(week = floor_date(date, "week")) %>%
  summarize(across(all_of(symbols), last))

weekly_returns <- weekly_prices %>%
  mutate(across(all_of(symbols), ~ log(. / lag(.)))) %>%
  drop_na()

monthly_prices <- prices_tibble %>%
  group_by(month = floor_date(date, "month")) %>%
  summarize(across(all_of(symbols), last))

monthly_returns <- monthly_prices %>%
  mutate(across(all_of(symbols), ~ log(. / lag(.)))) %>%
  drop_na()

monthly_returns_tibble <- as_tibble(monthly_returns)

monthly_returns_tibble <- monthly_returns_tibble %>%
  rename(date = month)

FFdata <- read.csv("https://mba.tuck.dartmouth.edu/pages/faculty/ken.french/ftp/F-F_Research_Data_Factors.CSV", skip = 3)

FFdata <- FFdata %>%
  mutate(date = parse_date_time(X, orders = "Y%m", quiet = TRUE)) %>%
  filter(!is.na(date)) %>%
  select(date, Mkt.RF, SMB, HML, RF) 

FFdata <- FFdata %>%
  mutate(across(-date, ~ as.numeric(gsub(" ", "", .))))

FFdata <- FFdata %>%
  mutate(date = as.Date(date))

merged_data <- left_join(monthly_returns_tibble, FFdata, by = 'date')

head(merged_data)
## # A tibble: 6 × 13
##   date           SPY     QQQ      EEM     IWM      EFA      TLT     IYR      GLD
##   <date>       <dbl>   <dbl>    <dbl>   <dbl>    <dbl>    <dbl>   <dbl>    <dbl>
## 1 2010-02-01  0.0307  0.0450  0.0176   0.0438  0.00266 -0.00343  0.0531  0.0322 
## 2 2010-03-01  0.0591  0.0743  0.0780   0.0791  0.0619  -0.0208   0.0930 -0.00440
## 3 2010-04-01  0.0154  0.0222 -0.00166  0.0552 -0.0284   0.0327   0.0619  0.0572 
## 4 2010-05-01 -0.0828 -0.0768 -0.0986  -0.0784 -0.119    0.0498  -0.0585  0.0301 
## 5 2010-06-01 -0.0531 -0.0616 -0.0141  -0.0806 -0.0208   0.0564  -0.0478  0.0233 
## 6 2010-07-01  0.0661  0.0701  0.104    0.0651  0.110   -0.00951  0.0899 -0.0522 
## # ℹ 4 more variables: Mkt.RF <dbl>, SMB <dbl>, HML <dbl>, RF <dbl>
capm_returns <- merged_data %>%
  filter(date >= "2010-02-01" & date <= "2015-01-31") %>%
  select(-date, -Mkt.RF, -SMB, -HML, -RF)

capm_cov_matrix <- cov(capm_returns)
print(capm_cov_matrix)
##               SPY           QQQ           EEM           IWM           EFA
## SPY  0.0013789625  0.0014370262  0.0017213328  0.0017634418  0.0015961646
## QQQ  0.0014370262  0.0017632634  0.0017694575  0.0018116904  0.0016582414
## EEM  0.0017213328  0.0017694575  0.0033901703  0.0023127663  0.0024955582
## IWM  0.0017634418  0.0018116904  0.0023127663  0.0026629366  0.0019648661
## EFA  0.0015961646  0.0016582414  0.0024955582  0.0019648661  0.0024254011
## TLT -0.0009663091 -0.0009584956 -0.0011821313 -0.0013080769 -0.0011039482
## IYR  0.0011816447  0.0012041807  0.0017966276  0.0015876779  0.0015471638
## GLD  0.0002043539  0.0003904111  0.0009310462  0.0005394854  0.0004417102
##               TLT           IYR          GLD
## SPY -0.0009663091  0.0011816447 0.0002043539
## QQQ -0.0009584956  0.0012041807 0.0003904111
## EEM -0.0011821313  0.0017966276 0.0009310462
## IWM -0.0013080769  0.0015876779 0.0005394854
## EFA -0.0011039482  0.0015471638 0.0004417102
## TLT  0.0015464545 -0.0003632202 0.0001797640
## IYR -0.0003632202  0.0019945635 0.0005353288
## GLD  0.0001797640  0.0005353288 0.0029025882
ff_returns <- merged_data %>%
  filter(date >= "2010-02-01" & date <= "2015-01-31")

residuals <- ff_returns %>%
  select(all_of(symbols)) %>%
  map_dfc(~ residuals(lm(. ~ Mkt.RF + SMB + HML, data = ff_returns)))

ff_cov_matrix <- cov(residuals)
print(ff_cov_matrix)
##               SPY           QQQ           EEM           IWM           EFA
## SPY  3.259798e-06  3.622417e-06  1.782285e-06  8.349164e-07  1.902441e-06
## QQQ  3.622417e-06  2.067120e-04 -5.274493e-05 -1.248073e-05 -3.610041e-05
## EEM  1.782285e-06 -5.274493e-05  1.213624e-03  4.639590e-05  5.052324e-04
## IWM  8.349164e-07 -1.248073e-05  4.639590e-05  1.656396e-05  3.183201e-05
## EFA  1.902441e-06 -3.610041e-05  5.052324e-04  3.183201e-05  5.327995e-04
## TLT  8.486413e-06 -4.926436e-06  1.964472e-05  2.785528e-05 -2.701087e-05
## IYR  2.136635e-05 -1.638250e-05  3.328144e-04  5.932313e-05  2.082001e-04
## GLD -8.119224e-06  5.140083e-05  5.668776e-04  5.843930e-05  1.954886e-04
##               TLT           IYR           GLD
## SPY  8.486413e-06  2.136635e-05 -8.119224e-06
## QQQ -4.926436e-06 -1.638250e-05  5.140083e-05
## EEM  1.964472e-05  3.328144e-04  5.668776e-04
## IWM  2.785528e-05  5.932313e-05  5.843930e-05
## EFA -2.701087e-05  2.082001e-04  1.954886e-04
## TLT  7.800141e-04  4.560212e-04  2.593792e-04
## IYR  4.560212e-04  1.008804e-03  3.079603e-04
## GLD  2.593792e-04  3.079603e-04  2.510801e-03
compute_gmv_weights <- function(cov_matrix) {
  inv_cov <- solve(cov_matrix)
  ones <- rep(1, nrow(inv_cov))
  weights <- inv_cov %*% ones / sum(inv_cov %*% ones)
  return(weights)
}

gmv_weights_capm <- compute_gmv_weights(capm_cov_matrix)
gmv_weights_ff <- compute_gmv_weights(ff_cov_matrix)

print(gmv_weights_capm)
##            [,1]
## SPY  0.94117585
## QQQ -0.18088752
## EEM -0.01437032
## IWM -0.05253371
## EFA -0.01342597
## TLT  0.48106233
## IYR -0.21174063
## GLD  0.05071999
print(gmv_weights_ff)
##              [,1]
## SPY  0.8299881359
## QQQ  0.0052274338
## EEM  0.0001171814
## IWM  0.1868608004
## EFA  0.0009310852
## TLT  0.0032734010
## IYR -0.0286058119
## GLD  0.0022077742