tracemem {base} | R Documentation

## Trace Copying of Objects

### Description

This function marks an object so that a message is printed whenever the internal code copies the object. It is a major cause of hard-to-predict memory use in R.

### Usage

    tracemem(x)
    untracemem(x)
    retracemem(x, previous = NULL)

### Arguments

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

### Details

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).

It is enabled in the CRAN macOS and Windows builds of R.

When an object is traced any copying of the object by the C function `duplicate` produces a message to standard output, as does type coercion and copying when passing arguments to `.C` or `.Fortran`.

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.

These functions are primitive.

### Value

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

### See Also

`capabilities("profmem")` to see if this was enabled for this build of R.

`trace`, `Rprofmem`

https://developer.r-project.org/memory-profiling.html

### Examples

    ## Not run:
    a <- 1:10
    tracemem(a)
    ## b and a share memory
    b <- a
    b[1] <- 1
    untracemem(a)

    ## copying in lm: less than R <= 2.15.0
    d <- stats::rnorm(10)
    tracemem(d)
    lm(d ~ a+log(b))

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

    ## End(Not run)

[Package base version 3.5.1 Index]