How to sample so sample includes 10% target variable = true and 90% target variable = false

[EC27556]

I have a 5m dataset.

95k have the target variable=1, the rest =0. I want to take a biased sample where I include all 95k cases and a selection of the =0 cases so the split will be 10% true and 90% false. Could anyone share some code to do this please?

Thanks

[PeterClemmensen]

So you want all the 95k 1's. And you want those 95k to be 10% of your resulting dataset, meaning that you want 950000 - 95000 of the remaining obs from your data?

[EC27556]

Yes,

Ultimately, I have 100 datasets and would like the sample to always have 10% hit and keep all target incidences where possible. So I want something I can loop for all datasets.

Unfortunately, sometimes I wont be able to use all of my target 'hit' observations because they already represent more than 10% of the aggregate datasets. in this case I would undersample the 'hits' to ensure I have 10% in the sample.

For the most part though, the datasets at an aggregate level have less than 10% of data that has a hit for the target variable. I would like some code to oversample the target variables so I can create a sample with 10% observations that have a hit.