Better log output about mlrmbo HOT 9 CLOSED

The problem is, that the helper function paramValueToString from the paramHelpers package forces 2 digit output for numeric parameters. I think we should add another parameter digits to paramValueToString with a default value of 2.

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To addresss your problem as a user: we should add a parameter like output.precision to mlrMBO to give the user control over number of digits.

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More important than the number of digits is the exponent of the parameter. You can add as many digits as you want, at some point every parameter is rounded to 0.0000..., but we want to see the difference between 1.24e-12 and 4.45e-12.
I'm fine with another parameter digits, but imho a parameter showExponent is more important.

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A parameter for the number of digits would be sufficient if we replace the conversion specification of sprintf form f to g used by paramValueToString. In the following example the number pf digits is fixed to 3:

sprintf("%.3f", 0.001)
# [1] "0.001"
sprintf("%.3g", 0.001)
# [1] "0.001"
sprintf("%.3f", 0.000000001)
# [1] "0.000"
sprintf("%.3g", 0.000000001)
# [1] "1e-09" <- This is what we want

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I would suggest this:

1. "%.3g"
   This is indeed what I usually use nowadays for such logging.

2. Number 1) should be a default setting in MBOControl.
   The user can overwrite it.
   Allow only one format now for all numerics in the logging line.
   [mbo] 0: cost=0.01; gamma=0.00; epsilon=0.00 : error=0.028, execTime=24374.496
   The default will be good 99% percent of the time.

3. To program 2) you need to make ParamHelpers::paramValueToString better.
   Introduce new arg "num.format", with default as in 1).

Is that it?

Assigned to Jakob.

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3. is exactly what I have already proposed :-)

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Sure, but as we can talk less currently, I try to be specific even if it is a bit redundant ;-)

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I am reading what is posted here and elsewhere

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I added the proposed parameter to ParamHelpers::paramValueToString with the corresponding default value. In mlrMBO there is now a output.num.format parameter in the control object which gives the possibility to influence the output.

@daniel: this should fix your issue.

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