R round to nearest .5 or .1

问题:

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.

回答1:

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

回答2:

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

回答3:

The taRifx package has just such a function:

> library(taRifx)
> roundnear( seq(.1,1,.13), c(.1,.1,.1,.2,.3,.3,.7) )
[1] 0.1 0.2 0.3 0.4 0.6 0.6 0.7

In your case, just feed it the stock price and the minimum tick increment as its first and second arguments, and it should work its magic.

N.B. This has now been deprecated. See comment.