How to create a new column which is less than the previous column value

I am trying to create a new column which is formed by taking the value from column A as the upper bound of the sample which I would like to take. I tried the following but no avail. Any suggestions? Suppose the value A is 15.25, then I would like to generate a value which is between 1 and 15.25 which are spaced by 1/4.

my_data = data.frame(A = sample(seq(1, 20, 1/4), 10))
my_data %>% mutate(B = sample(seq(1, A, 1/4), 1))

Solution

You can use rowwise that

allows you to compute on a data frame a row-at-a-time

as follows. Otherwise it would take the entire A column into sample where you need to specify only 1 value as upper-bound:

my_data %>% 
  rowwise() %>%
  mutate(B = sample(seq(1, A, 1/4), size = 1))

# A tibble: 10 × 2
# Rowwise: 
       A     B
   <dbl> <dbl>
 1 19     9.25
 2  8     6.25
 3  7.25  1.5 
 4  3.25  2.75
 5  2.75  2.25
 6 11     4   
 7 14.8  13   
 8  9.25  7.75
 9 10     9   
10 10.5   8.25