[R] how to randomly select the samples with different probabilities for different classes?

[Marna Wagley]

Hi R user,
I have samples with covariates for different classes, I wanted to choose
the samples of different groups with different probabilities. For example,
I have a 22 samples size with 3 classes,
groupA has 8 samples
groupB has 8 samples
groupC has 6 samples

I want to select a total 14 samples from 22 samples, in which  40% of the
14 samples should be in groups A and B, 60% of the 14 samples should be in
the group C.

Would you mind to help me on how I can select the samples with that
conditions? I have attached a sample data

dat<-structure(list(sampleID = c(17L, 21L, 36L, 45L, 67L, 82L, 90L,
31L, 70L, 45L, 24L, 80L, 82L, 45L, 85L, 14L, 81L, 96L, 61L, 12L,
65L, 88L), group = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("A",
"B", "C"), class = "factor")), .Names = c("sampleID", "group"
), class = "data.frame", row.names = c(NA, -22L))

thanks,
  MW

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