Easier Debugging of
One difficulty of
magrittr pipes is that they make
debugging harder. If you don't always write correct code, and you use
pipes, then you'll find
tamper very useful. It is the
alternative of the
recover function: when used with
options(error = tamper), after an error it displays the whole pipeline,
marks the place of the error, and helps saving the temporary results.
options(error = tamper::tamper)
Then, if you make a mistake in a pipeline, instead of the standard
R stack trace,
tamper is invoked and you can explore the data in
the pipeline, and also save to a temporary variable.
library(magrittr) 1:10 %>% multiply_by(10) %>% add(10) %>% add("oh no!") %>% subtract(5) %>% divide_by(5)
You will see:
Error in add(., "oh no!") : non-numeric argument to binary operator Enter 0 to exit or choose: 1: Switch mode 2: Take me to the error 3: 1:10 %>% 4: multiply_by(., 10) %>% 5: add(., 10) %>% 6: -> add(., "oh no!") %>% 7: subtract(., 5) %>% 8: divide_by(., 5) Selection:
The stage with the error is clearly marked with an arrow. You can get to
the function in which the error happened by selecting
2. (Unless it
is a primitive function, those are not in the call stack.)
If you select
6, you can browse the frame that corresponds to the
pipeline stage in which the error happened:
Selection: 6 Called from: eval(substitute(expr), envir, enclos) Browse> ls()  "function_list" "k" "value"
value is the value of the
. dot variable, at the beginning
of the pipeline stage:
Browse> value  20 30 40 50 60 70 80 90 100 110
If you don't want to redo the initial part of the pipeline, you
value to a global variable in your workspace:
Browse> assign("value", value, envir = globalenv())
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MIT © Gábor Csárdi.