Hi R-devel,
When using lapply upon data.frame, I notice lapply coerces data.frame to list
before calling internal lapply function.
R> lapply
function (X, FUN, ...)
{
FUN <- match.fun(FUN)
if (!is.vector(X) || is.object(X))
X <- as.list(X)
.Internal(lapply(X, FUN))
}
df <- data.frame(V1=seq(100*1024*1024), V2=rnorm(100*1024))
R> is.vector(df) # btw, list is a vector, data.frame is a list, but
data.frame is NOT a vector, something is not consistent ??
[1] FALSE
X <- as.list(X) is executed and takes time for large data.frame
R> object.size(df)
1258291976 bytes
R> system.time(as.list(df))
user system elapsed
1.396 0.472 1.885
The question is: Given that data.frame is a list, is it necessary to coerce the
data.frame to a list for lapply?
Would the following logic do the same but more efficient for lapply to run on
data.frame?
if (!is.vector(X) && !is.list(X) || is.object(X))
X <- as.list(X)
.Internal(lapply(X, FUN))
Thanks,
Qin
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