R round to nearest .5 or .1

Question

I have a data set of stock prices that have already been rounded to 2 decimal places (1234.56). I am now trying to round to a specific value which is different for each stock. Here are some examples:

Current Stock Price         Minimum Tick Increment       Desired Output   123.45                            .50                      123.50   155.03                            .10                      155.00   138.24                            .50                      138.00   129.94                            .10                      129.90    ...                              ...                       ... 

I'm not really sure how to do this but am open to suggestions.

Answer 1

I'm not familiar with R the language, but my method should work with any language with a ceiling function. I assume it's rounded UP to nearest 0.5:

a = ceiling(a*2) / 2  if a = 0.4, a = ceiling(0.4*2)/2 = ceiling(0.8)/2 = 1/2 = 0.5 if a = 0.9, a = ceiling(0.9*2)/2 = ceiling(1.8)/2 = 2/2 = 1 

Answer 2

Probably,

round(a/b)*b 

will do the work.

> a <- seq(.1,1,.13) > b <- c(.1,.1,.1,.2,.3,.3,.7) > data.frame(a, b, out = round(a/b)*b)      a   b out 1 0.10 0.1 0.1 2 0.23 0.1 0.2 3 0.36 0.1 0.4 4 0.49 0.2 0.4 5 0.62 0.3 0.6 6 0.75 0.3 0.6 7 0.88 0.7 0.7