tracemem {base}R Documentation

Trace Copying of Objects


This function marks an object so that a message is printed whenever the internal function duplicate is called. This happens when two objects share the same memory and one of them is modified. It is a major cause of hard-to-predict memory use in R.


retracemem(x, previous = NULL)


x An R object, not a function or environment or NULL.
previous A value as returned by tracemem or retracemem.


This functionality is optional, determined at compilation, because it makes R run a little more slowly even when no objects are being traced. tracemem and untracemem give errors when R is not compiled with memory profiling; retracemem does not (so it can be left in code during development).

When an object is traced any copying of the object by the C function duplicate or by arithmetic or mathmetical operations produces a message to standard output. The message consists of the string tracemem, the identifying strings for the object being copied and the new object being created, and a stack trace showing where the duplication occurred. retracemem() is used to indicate that a variable should be considered a copy of a previous variable (e.g. after subscripting).

The messages can be turned off with tracingState.

It is not possible to trace functions, as this would conflict with trace and it is not useful to trace NULL, environments, promises, weak references, or external pointer objects, as these are not duplicated.


A character string for identifying the object in the trace output (an address in hex enclosed in angle brackets), or NULL (invisibly for untracemem.

See Also

trace, Rprofmem


## Not run: 
a <- 1:10
## b and a share memory
b <- a
b[1] <- 1

## copying in lm
d <- rnorm(10)
lm(d ~ a+log(b))

## f is not a copy and is not traced
f <- d[-1]
## indicate that f should be traced as a copy of d
retracemem(f, retracemem(d))
## End(Not run)

[Package base version 2.5.0 Index]