[R] sapply on data frames - $X vs.["X"]

[Jacques VESLOT]

with apply loop, x is a vector you are indexing in the first sample code 
with its names.
so it failed when you tried indexing it with "$" which is dedicated to 
data frames.
 

Fernando Saldanha a écrit :

>I have a program where the following code works fine:
>
>df.opt$Delta <- apply(df.opt, 1, function(x)
>EuropeanOption(x["CallPutString"], x["UnderlyingPrice"],
>x["StrikePrice"], 0, interest.rate, x["FractionalExpiration"],
>x["Vol"])[[2]])
>
>However, the code below fails:
>
>#df.opt$Delta <- apply(df.opt, 1, function(x)
>EuropeanOption(x$CallPutString, #x["UnderlyingPrice"],
>x["StrikePrice"], 0, interest.rate, x["FractionalExpiration"],
>#x["Vol"])[[2]])
>
>Here df.opt is a data frame and European Option is a function in the
>package RQuantLib.
>The only difference between the two pieces of code is that a column of
>the data frame is accessed using "$" in the first case and brackets in
>the second case.
>
>Sorry if this is a trivial question, but could somebody tell me the
>reason for this behavior?
>
>FS
>
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