How to feed a list of unquoted column names into `lapply` (so that I can use it with a `dplyr` function)

Question

I am trying to write a function in tidyverse/dplyr that I want to eventually use with lapply (or map). (I had been working on it to answer

Answer 1

as.name will convert a string to a name and that can be passed to report:

lapply(cat.list, function(x) do.call("report", list(as.name(x))))

character argument An alternative is to rewrite report so that it accepts a character string argument:

report_ch <- function(colname) {  
    report_cat <- rlang::sym(colname)   # as.name(colname) would also work here
    sample_data %>%
                group_by(!!report_cat, YEAR) %>%
                summarize(num = n(), total = sum(AMOUNT)) %>% 
                rename(REPORT_VALUE = !!report_cat) %>% 
                mutate(REPORT_CATEGORY = colname)
}

lapply(cat.list, report_ch)

wrapr An alternate approach is to rewrite report using the wrapr package which is an alternative to rlang/tidyeval:

library(dplyr)
library(wrapr)

report_wrapr <- function(colname) 
  let(c(COLNAME = colname),
      sample_data %>%
                  group_by(COLNAME, YEAR) %>%
                  summarize(num = n(), total = sum(AMOUNT)) %>%
                  rename(REPORT_VALUE = COLNAME) %>%
                  mutate(REPORT_CATEGORY = colname)
   )

lapply(cat.list, report_wrapr)

Of course, this whole problem would go away if you used a different framework, e.g.

plyr

library(plyr)

report_plyr <- function(colname)
  ddply(sample_data, c(REPORT_VALUE = colname, "YEAR"), function(x)
     data.frame(num = nrow(x), total = sum(x$AMOUNT), REPORT_CATEOGRY = colname))

lapply(cat.list, report_plyr)

sqldf

library(sqldf)

report_sql <- function(colname, envir = parent.frame(), ...)
  fn$sqldf("select [$colname] REPORT_VALUE,
                   YEAR,
                   count(*) num,
                   sum(AMOUNT) total,
                   '$colname' REPORT_CATEGORY
            from sample_data
            group by [$colname], YEAR", envir = envir, ...)

lapply(cat.list, report_sql)              

base - by

report_base_by <- function(colname)
      do.call("rbind", 
        by(sample_data, sample_data[c(colname, "YEAR")], function(x)
            data.frame(REPORT_VALUE = x[1, colname], 
                       YEAR = x$YEAR[1], 
                       num = nrow(x), 
                       total = sum(x$AMOUNT), 
                       REPORT_CATEGORY = colname)
         )
      )

lapply(cat.list, report_base_by)

data.table The data.table package provides another alternative but that has already been covered by another answer.

Update: Added additional alternatives.