在 while 循环中条件应用函数的 R 问题

问：

我对以下代码有问题（见下文）。 在代码的末尾，我计划了一个 while 循环（请参阅代码中的注释）。但是，当我手动测试它时，该循环不起作用（即多次运行代码）。

library(dplyr)

# Generate data
df = data.frame(var_a = c('A',NA, NA,'A',NA, NA, NA,NA, NA, NA),
                var_b = c('B','B',NA, NA,NA, NA, NA,NA, NA, NA),
                var_c = c(NA,'C','C',NA,NA, NA, NA,NA, NA, NA),
                var_d = c('D',NA,'D','D',NA, NA, NA,NA, NA, NA),
                var_e = c(NA,'Text',NA,'Text','Text', 'Text', NA,NA, 'Text', NA))


# Function to test if all values in a row from a specified list of variable equal NA
test_all_na <- function(df, na_test_vars){
  df_test <- df %>%
    mutate(all_na = rowSums(is.na(.[na_test_vars])) == length(na_test_vars))
  return(df_test)
}

# Specify variables to test if all values in a row equal NA
na_test_vars <- c("var_a", "var_b", "var_c", "var_d")                

# Generate new variable in df with logical vector if all values equal NA
df <- test_all_na(df, na_test_vars)


# Function to select randomly one value from a list of values based on probabilities
select_value <- function(old_value, prob, list_of_values){
  new_value <- sample(list_of_values, 
                      size = 1,
                      prob = prob)
  return(new_value)
}

# Set condition to change values 
condition <- df$all_na == TRUE

# Count occurances of TRUE in variable all_na
counter = sum(df$all_na)
print(counter)

### HERE SHOULD COME A WHILE LOOP: while counter > 0
# replace values with select_values function in various variables based on the condition
df$var_a <- ifelse(condition, sapply(df$var_a, select_value, prob = c(0.2, 0.8), list_of_values = c('A', NA)), df$var_a)
df$var_b <- ifelse(condition, sapply(df$var_b, select_value, prob = c(0.2, 0.8), list_of_values = c('B', NA)), df$var_b)
df$var_c <- ifelse(condition, sapply(df$var_c, select_value, prob = c(0.2, 0.8), list_of_values = c('C', NA)), df$var_c)
df$var_d <- ifelse(condition, sapply(df$var_d, select_value, prob = c(0.2, 0.8), list_of_values = c('D', NA)), df$var_d)

# Generate again variable in df with logical vector if all values equal NA
df <- test_all_na(df, na_test_vars)

# Count occurances of TRUE in variable all_na
counter = sum(df$all_na)
print(counter)

### END WHILE LOOP

第一次工作。在循环之前，有 6 条线在指定的变量中都等于 NA。在那之后，只有更少的行（取决于机会）。我实际期望的是，每次运行时，满足条件的行数都会减少。但事实并非如此。总是有不同的数字，有时更多，有时更少。所以循环到无穷大。你知道我做错了什么吗？感谢您的帮助！