How can I use for loop inside shiny server? - r

Question

This is my very first question here, can anybody help me to solve this problem? I will really appreciate that!
I am trying to create a vector based on existing vectors. But the for loop inside shiny server didn't work for me. I have tried many ways but still cannot make it.
ui <- (
tabPanel(
"Momentum Analysis",
sidebarPanel(
width = 4,
textInput("ticker2", "Stock ticker:"),
dateRangeInput(
"date2",
"Date Range:",
max = Sys.Date(),
end = Sys.Date(),
startview = "year"
),
numericInput(
"alpha",
"Volatility smoothing parameter:",
min = 0,
max = 1,
value = 0.05
),
numericInput(
"beta",
"Momentum smoothing parameter:",
min = 0,
max = 1,
value = 0.05
),
radioButtons("type2",
"Chart Type:",
c(
"Momentum vs. Volatility" = "mvv",
"Signal to Noise Ratio" = "snr"
)),
actionButton(
"plot2",
"Plot",
icon("line-chart"),
style = "color: #fff;
background-color: #337ab7;
border-color: #2e6da4"
),
div(
style = "display: inline-block;
vertical-align: top",
downloadButton("download2", "Download historical stock price data")
)
),
mainPanel(plotOutput("chart2"))
)
)
)
server <- function(input, output){
stock2 <-
reactive(
getSymbols(
toupper(input$ticker2),
from = as.Date(input$date2[1]) - 150,
to = input$date2[2],
src = "google",
auto.assign = F
)
)
stock3 <- reactive(as.data.table(stock2()))
stock <- reactive(as.data.frame(stock3()))
stock.return <- reactive(diff(log(stock()[, 5])))
stock.mu <- reactive(mean(stock.return()))
stock.var <- reactive((stock.return() - stock.mu()) ^ 2)
stock.var.smoothed <- reactive(rep(0, length(stock.return())))
stock.var.smoothed <- reactive({
for (i in 2:length(stock.var())) {
stock.var.smoothed[1] <- stock.var()[1]
stock.var.smoothed[i] <-
(1 - input$alpha) * stock.var.smoothed()[i - 1] + input$alpha * stock.var()[i]
}
})
stock.std.smoothed <- reactive(sqrt(stock.var.smoothed()))
stock.std.smoothed.annually <- reactive(stock.var.smoothed() * sqrt(252))
stock.momentum <- reactive(stock.return())
stock.momentum.smoothed <- reactive(rep(0, length(stock.return())))
stock.momentum.smoothed <- reactive({
for (i in 2:length(stock.return())) {
stock.momentum.smoothed[1] <- stock.momentum()[1]
stock.momentum.smoothed[i] <-
(1 - input$beta) * stock.momentum.smoothed()[i - 1] + input$beta * stock.return()[i]
}
})
stock.momentum.smoothed.annually <-
reactive(stock.momentum.smoothed() * 252 / 100)
stock.SNR <-
reactive(stock.momentum.smoothed.annually() / stock.std.smoothed.annually())
output$chart2 <- renderPlot({
req(input$plot2)
if (input$type2 == "mvv"){
plot(
stock.momentum.smoothed(),
main = "Momentum v.s. Volatility",
col = "red",
type = "l",
xaxt = "n",
ylab = "Momentum v.s. Volatility",
xlab = "Date",
ylim = c(-2, 2)
)
lines(stock.std.smoothed())
axis(1, at = 1:length(stock()[, 1]), labels = stock()[, 1])
}
else if (input$type2 == "snr"){
plot(
stock.SNR(),
main = "Signal to Noise",
type = "l",
col = "red",
ylim = c(-1, 1),
xaxt = "n",
ylab = "Signal to Noise Ratio",
xlab = "Date"
)
abline(h = 0.5)
axis(1, at = 1:length(stock()[, 1]), labels = stock()[, 1])
}
})
output$download2 <- downloadHandler(
filename = function() {
paste(toupper(input$ticker2),
" ",
input$date2[1],
" ",
input$date2[2],
".xlsx",
sep = "")
},
content = function(file) {
write.xlsx2(stock2()[paste0(input$date2, "/"),], file)
}
)
}
I am trying to plot the stock's momentum vs volatility, both are smoothed. My app has some other tabs but they are irrelevant so I just hided the code.
The only problem here is the loop and the reactive function. Thank you!

Answer 1

Please refer to Konrad Rudolph's answer
For loop inside reactive function in Shiny
I was trying to assign a vector with a function (reactive). But I didn't give any return to that function and so that I cannot call this function.