When mapply is applied to a function that has a call to browser() within
it, the result can be a disastrous amount of feedback.
To clarify this situation please consider the following function,
containing a call to browser within it:
plus = function(a, b) {browser(); a + b}
A plain vanilla call to plus() yields the following:
LAPTOP_32G_01> plus(1,2)
Called from: plus(1, 2)
Browse[1]>
[1] 3
Now consider the following application of mapply to plus:
LAPTOP_32G_01> mapply(plus, 1:2, 1:2)
Called from: (function (a, b)
{
browser()
a + b
})(dots[[1L]][[1L]], dots[[2L]][[1L]])
Browse[1]>
Called from: (function (a, b)
{
browser()
a + b
})(dots[[1L]][[2L]], dots[[2L]][[2L]])
Browse[1]>
[1] 2 4
Notice that at each step, after the browser is called, mapply prints out
the function call including its arguments:
Called from: (function (a, b)
{
browser()
a + b
})(dots[[1L]][[1L]], dots[[2L]][[1L]])
etc.
In the present case this does no harm except to make things a little harder
to read. However, if one of the inputs happens to be a data frame with a
million rows, the entire million rows are printed to the screen. I have
been bitten by this, which is why I am writing this note. I have a question
and a request:
Question: Is there some way to prevent mapply (or browser) from echoing the
function call when browser is called from within FUN?
Request: If not, could the ability to turn off this echoing be provided. As
things stand, calling browser from within FUN, when FUN is a realistically
big function or has realistically big arguments, is a disaster.
Thanks.
[[alternative HTML version deleted]]
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