Generalizable function to select and filter dataframe r - using shiny input

Question

I am building a shiny app. The user will need to be able to reduce the data by selecting variables and filtering on specific values for those variables. I am stuck trying to get a generalizable function that can work based on all possible selections.

Here is an example - I skip the shiny code because I think the problem is with the function:

#sample dataframe
df <- data.frame('date' = c(1, 2, 3, 2, 2, 3, 1), 
                 'time' = c('a', 'b', 'c', 'e', 'b', 'a', 'e'), 
                 'place' = c('A', 'A', 'A', 'H', 'A', 'H', 'H'), 
                 'result' = c('W', 'W', 'L', 'W', 'W', 'L', 'L'))

If the user selected date and result for the date values 1, 2; and the result values W, I would do the following:

out <- df %>%
    select(date, result) %>%
    filter(date %in% c(1,2)) %>%
    filter(result %in% c('W'))

The challenge I am having is that the user can select any unique combinations of variables and values. Using the input$ values from my shiny app, I can get the selected variables into a vector and I can get the selected values into a list of values, positionaly matching the selected variables. For example:

selected_variables <- c('date', 'result')
selected_values <- list(c(1,2), c('W'))

What i think i then need is a generalizable function that will match up the filter calls with the correct variables. Something like:

#function that takes data frame, vector of selected variables, list of vectors of chosen values for each variable
#Returns a reduced table of selected variables, filtered values
table_reducer <- function(df, select_var, filter_values) { 
    #select the variables        
    out <- df %>%
    #now filter each variable by the values contained in the list
    select(vect_of_var)
    out <- [for loop that iterates over vect_of_var, list_of_vec, filtering accordingly]
    out #return out
}

My thinking would be to use a zip equivalent from python, but all my searching on that just points me to mapply and i can't see how to use that within the for loop (which i also know is not always approved in R - but i am talking about a relatively small number of iterations). If there is a better solution to this i would welcome it.

user_3962914 · Answer

Here's a 1-liner table_reducer function in base R -

table_reducer <- function(df, select_var, filter_values) {
  subset(df, Reduce(`&`, Map(`%in%`, df[select_var], filter_values)))  
}

selected_variables <- c('date', 'result')
selected_values <- list(c(1,2), c('W'))
table_reducer(df, selected_variables, selected_values)

#  date time place result
#1    1    a     A      W
#2    2    b     A      W
#4    2    e     H      W
#5    2    b     A      W

Map is a wrapper over mapply so you were right in thinking that you should use mapply for this task. This answer is also free of dreaded for loops.

Generalizable function to select and filter dataframe r - using shiny input

1 Answers