Cannot resolve "Warning: Factor `officialTitle` contains implicit NA, consider using `forcats::fct_explicit_na`"

Question

I tried the following. Why do I still get forcats warning?

#1 I execute

plotdata <- dplyr::filter(Marriage, FALSE) %>% count(officialTitle)

  if (nrow(plotdata) > 0){
    str <- paste("nrows > 0. Number of rows is ", nrow(plotdata))
    print(str)
    print(plotdata)

But I get the following:

[1] "nrows > 0. Number of rows is  1"
# A tibble: 1 x 2
  officialTitle     n
  <fct>         <int>
1 NA                0
Warning message:
Factor `officialTitle` contains implicit NA, consider using `forcats::fct_explicit_na`

#2 I heed the warning and execute the following

plotdata <- dplyr::filter(Marriage, FALSE) %>% count(officialTitle)
plotdata$officialTitle <- fct_explicit_na(plotdata$officialTitle)

  if (nrow(plotdata) > 0){
    str <- paste("nrows > 0. Number of rows is ", nrow(plotdata))
    print(str)
    print(plotdata)

This is the result:

[1] "nrows > 0. Number of rows is  1"
# A tibble: 1 x 2
  officialTitle     n
  <fct>         <int>
1 (Missing)         0
Warning message:
Factor `officialTitle` contains implicit NA, consider using `forcats::fct_explicit_na` 

#3 Then I think maybe this has nothing to do with forcats. I delete the forcats statement and remove na from plotdata, ie

plotdata <- dplyr::filter(Marriage, FALSE) %>% count(officialTitle)
plotdata <- na.omit(plotdata)

  if (nrow(plotdata) > 0){
    str <- paste("nrows > 0. Number of rows is ", nrow(plotdata))
    print(str)
    print(plotdata)

Output is following:

[1] "nrows < 0. Number of rows is  0"
# A tibble: 0 x 2
# ... with 2 variables: officialTitle <fct>, n <int>
Warning message:
Factor `officialTitle` contains implicit NA, consider using `forcats::fct_explicit_na`

Complete Code:

# Load packages ----
library(shiny)
library(ggplot2)
library(dplyr)
library(scales)
library(treemapify)
library(forcats)

# Load data ----
data(Marriage, package="mosaicData")

plotdata <- dplyr::filter(Marriage, FALSE) %>% count(officialTitle)
#plotdata$officialTitle <- fct_explicit_na(plotdata$officialTitle)
plotdata <- na.omit(plotdata)

  if (nrow(plotdata) > 0){
    str <- paste("nrows > 0. Number of rows is ", nrow(plotdata))
    print(str)
    print(plotdata)
    ggplot(plotdata, 
           aes(fill = officialTitle, 
               area = n,
               label = officialTitle)) +
      geom_treemap() + 
      geom_treemap_text(colour = "white", 
                        place = "centre") +
      labs(title = "Marriages by officiate") +
      theme(legend.position = "none")
  } else {
    str <- paste("nrows < 0. Number of rows is ", nrow(plotdata))
    print(str)
    print(plotdata)
  }

Answer 1

The error message isn't raised by forcats. In your case it results from counting an empty df. Try this:

# Empty dataframe
df <- data.frame(x = factor(integer(0))) 

# Count empty column
dplyr::count(df, x)
#> Warning: Factor `x` contains implicit NA, consider using
#> `forcats::fct_explicit_na`
#> # A tibble: 1 x 2
#>   x         n
#>   <fct> <int>
#> 1 <NA>      0

# To avoid the warning use .drop = FALSE which also results in an empty df

dplyr::count(df, x, .drop = FALSE)
#> # A tibble: 0 x 2
#> # ... with 2 variables: x <fct>, n <int>

^{Created on 2020-04-14 by the reprex package (v0.3.0)}

With the Marriage dataset:

# Load data ----
library(dplyr)

data(Marriage, package="mosaicData")

dplyr::filter(Marriage, FALSE) %>% count(officialTitle)
#> Warning: Factor `officialTitle` contains implicit NA, consider using
#> `forcats::fct_explicit_na`
#> # A tibble: 1 x 2
#>   officialTitle     n
#>   <fct>         <int>
#> 1 <NA>              0

dplyr::filter(Marriage, FALSE) %>% count(officialTitle, .drop = FALSE)
#> # A tibble: 9 x 2
#>   officialTitle           n
#>   <fct>               <int>
#> 1 "BISHOP"                0
#> 2 "CATHOLIC PRIEST"       0
#> 3 "CHIEF CLERK"           0
#> 4 "CIRCUIT JUDGE "        0
#> 5 "ELDER"                 0
#> 6 "MARRIAGE OFFICIAL"     0
#> 7 "MINISTER"              0
#> 8 "PASTOR"                0
#> 9 "REVEREND"              0

^{Created on 2020-04-14 by the reprex package (v0.3.0)}