check the help file. ?aggregate says that it ignores missing values by
default ;)
df <- read.table( header = TRUE , text = "FID MID IID EW_INCU
EW_17.5 EMW EEratio
1 4621 TWF2H5 45.26 NA 15.61 NA
1 4621 TWF2H6 48.02 44.09 13.41 0.3041506
2 4630 TWF2H19 51.44 47.81 NA NA
2 4631 TWF2H21 NA 52.72 16.70 0.3167678
2 4632 TWF2H22 55.70 50.45 16.48 0.3266601
2 4633 TWF2H23 44.42 40.89 12.96 0.3169479"
)
aggregate( . ~ FID , data = df , mean )
# na.rm would need to be passed to tapply, which is a similar function
tapply( df[ , 4 ] , df[ , 1 ] , mean )
tapply( df[ , 4 ] , df[ , 1 ] , mean , na.rm = TRUE )
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