Reactive Function - r

Question

Prior to start creating my app with Shiny I've created a function (NextWordPrediction) that updates my dataframe based on an user's input as follows:
If input exists in df increase its Frequency by 1
If input does't exist in df add it
Function code:
NextWordPrediction <- function(input) {
dat <- dat %>%
filter(., N_gram == str_count(input, "\\S+") + 1) %>%
filter(grepl(paste("^", tolower(str_squish(input)), sep = ""), Word)) %>%
arrange(., desc(Prop))
if (nrow(dat) != 0) {
assign("dat",
dat %>%
mutate(Frequency = ifelse(Word == input &
N_gram == str_count(input, "\\S+"),
Frequency + 1,
Frequency)) %>%
group_by(., N_gram) %>%
mutate(., Prop = Frequency/ sum(Frequency)) %>%
data.frame(.),
envir = .GlobalEnv)
val <- dat$Word_to_Predict[1]
ans <- paste(str_squish(input), val)
return(list(ans, head(dat,5)))
} else if (nrow(dat) == 0 & word(input, 1) != "NA") {
assign("dat",
dat %>%
add_row(., Word = tolower(input), Frequency = + 1, N_gram = str_count(input, "\\S+"),
Word_to_Predict = word(input, -1)) %>%
group_by(., N_gram) %>%
mutate(., Prop = Frequency/ sum(Frequency)) %>%
data.frame(.),
envir = .GlobalEnv)
input_1 <- Reduce(paste, word(input, 2:str_count(input,"\\S+")))
return(NextWordPrediction(input_1))
} else if (word(input, 1) == "NA") {
ans <- paste("Word not in dictionary. We added this to our database!")
return(ans)
}
}
As a next step I want to extend this functionality to a Shiny app and I've tried the following without success. The function usability is functional but after an input my df is not updated accordingly.
server.R
library(shiny)
dat <- read.csv("dat_all.csv")
shinyServer(function(input, output) {
NextWordPrediction <- function(input) {
dat <- dat %>%
filter(., N_gram == str_count(input, "\\S+") + 1) %>%
filter(grepl(paste("^", tolower(str_squish(input)), sep = ""), Word)) %>%
arrange(., desc(Prop))
if (nrow(dat) != 0) {
assign("dat",
dat %>%
mutate(Frequency = ifelse(Word == input &
N_gram == str_count(input, "\\S+"),
Frequency + 1,
Frequency)) %>%
group_by(., N_gram) %>%
mutate(., Prop = Frequency/ sum(Frequency)) %>%
data.frame(.),
envir = .GlobalEnv)
val <- dat$Word_to_Predict[1]
ans <- paste(str_squish(input), val)
return(list(ans, head(dat,5)))
} else if (nrow(dat) == 0 & word(input, 1) != "NA") {
assign("dat",
dat %>%
add_row(., Word = tolower(input), Frequency = + 1, N_gram = str_count(input, "\\S+"),
Word_to_Predict = word(input, -1)) %>%
group_by(., N_gram) %>%
mutate(., Prop = Frequency/ sum(Frequency)) %>%
data.frame(.),
envir = .GlobalEnv)
input_1 <- Reduce(paste, word(input, 2:str_count(input,"\\S+")))
return(NextWordPrediction(input_1))
} else if (word(input, 1) == "NA") {
ans <- paste("Word not in dictionary. We added this to our database!")
return(ans)
}
}
output$predictiontext = reactive({
NextWordPrediction(input$text)[1]
})
output$predictiontable = renderTable({
NextWordPrediction(input$text)[2]
})
})
ui.R
library(shiny)
# Define UI for application that draws a histogram
shinyUI(fluidPage(
# Application title
titlePanel("NextWordPrediction"),
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
textInput("text",
"Type something...",
"")
),
# Show a plot of the generated distribution
mainPanel(
wellPanel(
# Link to report
helpText(a('More information on the app',
href=link,
target = '_blank')
),
# Link to repo
helpText(a('Code repository',
href=link,
target = '_blank')
),
textOutput("predictiontext"),
tableOutput('predictiontable')
)
)
))
)
Update 1: Data
df<- data.frame(Word = c("hello", "she was great", "this is", "long time ago in"), Frequency = c(4, 3, 10, 1),
N_gram = c(1, 3, 2, 4), Prop = c(4/18, 3/18, 10/18, 1/18), Word_to_Predict = c(NA, "great", "is", "in"))
NextWordPrediction("she was") ## returns "she was" & "great"
NextWordPrediction("hours ago") ## returns "hours ago" & "in"
NextWordPrediction("words not in data") ## returns "Word not in dictionary. We added this to our database!" after trying "not in data", "in data" and adds "words not in data" to dataset