Extract the maximum value within each group in a dataframe

Question

I have a data frame with a grouping variable   Gene   and a value variable   Value     Gene   Value A      12 A      10 B      3 B      5 B      6 C      1 D      3 D      4   For each level of my grouping variable  I wish to extract the maximum value  The result should thus be a data frame with one row per level of the grouping variable   Gene   Value A      12 B      6 C      1 D      4   Could aggregate do the trick

User · Answer

df Gene  lt - as factor df Gene  do call rbind  lapply split df df Gene   function x   return x which max x Value          Just using base R

User · Answer

Using sqldf and standard sql to get the maximum values grouped by another variable  https   cran r-project org web packages sqldf sqldf pdf  library sqldf  sqldf  select max Value  Gene from df1 group by Gene     or  Using the excellent Hmisc package for a groupby application of function  max  https   www rdocumentation org packages Hmisc versions 4 0-3 topics summarize  library Hmisc  summarize df1 Value df1 Gene max

User · Answer

There are many possibilities to do this in R  Here are some of them   df  lt - read table header   TRUE  text    Gene   Value A      12 A      10 B      3 B      5 B      6 C      1 D      3 D      4      aggregate aggregate df Value  by   list df Gene   max  aggregate Value   Gene  data   df  max     tapply tapply df Value  df Gene  max     split   lapply lapply split df  df Gene   function y  max y Value      plyr require plyr  ddply df    Gene   summarise  Value   max Value      dplyr require dplyr  df   gt   group by Gene    gt   summarise Value   max Value      data table require data table  dt  lt - data table df  dt    max Value   by   Gene     doBy require doBy  summaryBy Value Gene  data   df  FUN   max     sqldf require sqldf  sqldf  select Gene  max Value  as Value from df group by Gene   drv    SQLite      ave df as logical ave df Value  df Gene  FUN   function x  x    max x

[r] Extract the maximum value within each group in a dataframe

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