Sample using start and end values within a loop in R

Question

I am trying to sample between a range of values as part of a larger loop in R. As the loop progresses to each row j, I want to sample a number between the value giv

Answer 1

You might not need to loop through. If you want need is something between start and end, it's almost equivalent to sampling something between 0-1 and multiplying that by the range.

df %>% mutate(sampled = start + round((end-start)*runif(nrow(.))))

Regarding the updating, dependencies you mentioned in your comment: sounds a bit complicated. Quick thought: Might be faster to sample a lot of times and choose one that fits your criteria.

Answer 2

First, put the data in a format that is easier to use with dput(df):

df <- structure(list(ID = structure(1:14, .Label = c("a", "b", "c", 
    "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n"), class = "factor"), 
    start = c(25L, 36L, 23L, 15L, 21L, 43L, 39L, 27L, 11L, 21L, 
    28L, 44L, 16L, 25L), end = c(67L, 97L, 85L, 67L, 52L, 72L, 
    55L, 62L, 99L, 89L, 65L, 58L, 77L, 88L), sampled = c(44L, 
    67L, 77L, 52L, 41L, 66L, 49L, 35L, 17L, 66L, 48L, 48L, 22L, 
    65L)), class = "data.frame", row.names = c(NA, -14L))

You were very close with mapply() but you made it harder than it needs to be:

df$sampled <- mapply(function(x, y) sample(seq(x, y), 1), df$start, df$end)
df
#    ID start end sampled
# 1   a    25  67      67
# 2   b    36  97      86
# 3   c    23  85      54
# 4   d    15  67      36
# 5   e    21  52      37
# 6   f    43  72      60
# 7   g    39  55      44
# 8   h    27  62      37
# 9   i    11  99      86
# 10  j    21  89      52
# 11  k    28  65      65
# 12  l    44  58      51
# 13  m    16  77      62
# 14  n    25  88      31

Answer 3

Figured it out. df[j,4] <- mapply(function(x, y) sample(seq(x, y), 1), df[j,"start"], df[j,"end"])

I just needed to be specific as to which row of the sampled values I wanted to enter into df[j,4]. Specifying row j for columns start and end did the trick.