Subset data based on Minimum Value

Question

This might an easy one. Here\'s the data:

dat <- read.table(header=TRUE, text=\"
Seg  ID  Distance
Seg46      V21 160.37672
Seg72      V85 191.24400
Seg37         


        

Answer 1

We can subset the rows with which.min. After grouping with 'ID', we slice the rows based on the position of minimum 'Distance'.

library(dplyr)
dat %>% 
   group_by(ID) %>% 
   slice(which.min(Distance))

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A similar option using data.table would be

library(data.table)
setDT(dat)[, .SD[which.min(Distance)], by = ID]

Answer 2

If you prefer ddply you could do this

library(plyr)
ddply(dat, .(ID), summarize, 
      Seg = Seg[which.min(Distance)], 
      Distance = min(Distance))

#    ID    Seg  Distance
#1 V147 Seg159  14.74852
#2 V171 Seg233 193.01636
#3  V21  Seg46 160.37672
#4  V85 Seg373 167.38930