R how to find maximum value by a primary key and removing duplicates -

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this question has answer here:

i have dataset below , want reduce removing rows. in situation have more 1 attach value same exact combination of first 3 columns, want keep rows have maximum attach value

bom = c(rep("bom1", 1), rep("bom2", 2), rep("bom3", 3)) part = c(rep("a", 3), rep("d", 3)) ww = c(rep("ww01",3),rep("ww05",1),rep("ww06",2)) attach = c(1,4,8,2,2,4)   df1 = data.frame(bom,part,ww,attach )

the final output have row numbers 1,3,4,6 , remaining rows deleted

you can dplyr:

library(dplyr) df1 %>% group_by(bom, part, ww) %>% summarise(attach = max(attach)) source: local data frame [4 x 4] groups: bom, part     bom part   ww attach 1 bom1    ww01      1 2 bom2    ww01      8 3 bom3    d ww05      2 4 bom3    d ww06      4

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