library(rbiom)
    library(dplyr)
    
    # Subset to specific samples
    biom <- hmp50[c('HMP20', 'HMP42', 'HMP12')]
    biom$metadata
    
    # Subset to specific OTUs
    biom <- hmp50[c('LtbAci52', 'UncO2012'),] # <- Trailing ,
    biom$taxonomy
    
    # Subset to specific samples and OTUs
    biom <- hmp50[c('LtbAci52', 'UncO2012'), c('HMP20', 'HMP42', 'HMP12')]
    as.matrix(biom)
    
    # Subset samples according to metadata
    biom <- subset(hmp50, `Body Site` %in% c('Saliva') & Age < 25)
    biom$metadata
    
    # Subset OTUs according to taxonomy
    biom <- subset_taxa(hmp50, Phylum == 'Cyanobacteria')
    biom$taxonomy
    
    # Remove samples with NA metadata values
    biom <- mutate(hmp50, BS2 = na_if(`Body Site`, 'Saliva'))
    biom$metadata
    biom <- na.omit(biom)
    biom$metadata
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