how to know which function is associated with which package in rstats

Typically speaking we don't specify the package before a function because it's not needed and it's less writing. That does not mean that it's not possible however. You can use the notation package_name::function_name() to load functions from packages without even the need to library() them. This is mostly used when loaded packages have overlapping function names.

To get a list of all functions used in a certain code the package NCmisc has a very handy function:

NCmisc::list.functions.in.file("app.R")

$.GlobalEnv
[1] "dt.data"

$`c("package:lubridate", "package:data.table")`
[1] "isoweek" "month"   "year"   

$`character(0)`
 [1] "."             "dt.Cycle"      "dt.filter"     "dt.KPI"        "dt.monthly"    "dt.MQQ"        "dt.overunder"  "dt.shops"      "dt.sorterrfid" "dt.WO"         "dt.YTD"       

$`package:base`
 [1] "as.Date"  "c"        "library"  "list"     "max"      "order"    "paste"    "paste0"   "readRDS"  "round"    "sum"      "Sys.Date"

$`package:billboarder`
[1] "bb_legend"         "bb_linechart"      "bb_x_axis"         "bb_y_axis"         "bb_y_grid"         "bbaes"             "billboarder"       "billboarderOutput" "renderBillboarder"

$`package:data.table`
[1] "melt.data.table" "setcolorder"    

$`package:shiny`
 [1] "br"                 "checkboxGroupInput" "conditionalPanel"   "dataTableOutput"    "div"                "downloadButton"     "downloadHandler"    "numericInput"       "radioButtons"      
[10] "reactive"           "renderDataTable"    "selectInput"        "shinyApp"           "tabPanel"           "tabsetPanel"       

$`package:shinydashboard`
[1] "dashboardBody"    "dashboardHeader"  "dashboardPage"    "dashboardSidebar"

$`package:utils`
[1] "write.csv"

When using this function just make sure that you have the packages loaded. It can only check the function names in packages that are in your loaded library.