Calculating log returns using R

  • I am trying to calculate the log returns of a dataset in R using the usual log differencing method. However, the calculated data is simply a vector of zeroes. I can't see what I'm doing wrong.

    Here is the snippet showing what I'm doing

    > prices <- data$cl
    > head(prices)
    [1] 1108.1 1095.4 1095.4 1102.2 1096.3 1096.7
    >
    >
    > lrets <- log(lag(prices)) - log(prices)
    > head(lrets)
    [1] 0 0 0 0 0 0
    > summary(lrets)
       Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
          0       0       0       0       0       0 
    

    What am I doing wrong?

    lrets <- diff(log(prices))

    @VishalBelsare you should add that as an answer.

    @Patrick Burns, vonjd, aajajim thanks to all of you for answering. I learned new information.

  • Nemis

    Nemis Correct answer

    9 years ago

    You are simply doing $log(S_t) - log(S_t) = 0$ for all $t$. Instead, try

    > n <- length(prices);
    > lrest <- log(prices[-1]/prices[-n])
    

    Should do the trick.

    Or the more traditional, fewer characters: diff(log(prices)) which also works when 'prices' is a matrix with times in the rows and assets in the columns. The other lesson is that 'lag' doesn't do what we naively expect it to do.

    To be sure that `lag` works as you expect, it is much safer to store your time series as `zoo` or `xts` objects: if you use vectors (or even `ts` objects), many operations will discard or ignore the timestamps.

    hadnt noticed the "diff" function yet. A handy one, indeed.

    @PatrickBurns: +1 for your input. I preferred your more succinct syntax. Would have accepted that as an answer.

    i have been using diff(log(prices)) for a while, but was starting to doubt as it seems almost noone use it. thanks :)

    There was a slight (obvious?) error in my reply with taking the negative logreturn instead. Now corrected. Thanks to user6569 that notified me.

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Content dated before 7/24/2021 11:53 AM