r - Why does summarise on grouped data result in only overall summary in dplyr? -

suppose have following data:

dfx <- data.frame(   group = c(rep('a', 8), rep('b', 15), rep('c', 6)),   sex = sample(c("m", "f"), size = 29, replace = true),   age = runif(n = 29, min = 18, max = 54) ) 

with old plyr can create little table summarizing data following code:

require(plyr) ddply(dfx, .(group, sex), summarize,       mean = round(mean(age), 2),       sd = round(sd(age), 2)) 

the output this:

  group sex  mean    sd 1       f 49.68  5.68 2       m 32.21  6.27 3     b   f 31.87  9.80 4     b   m 37.54  9.73 5     c   f 40.61 15.21 6     c   m 36.33 11.33 

i'm trying move code dplyr , %>% operator. code takes df group group , sex , summarise it. is:

dfx %>% group_by(group, sex) %>%    summarise(mean = round(mean(age), 2), sd = round(sd(age), 2)) 

but output is:

  mean   sd 1 35.56 9.92 

what doing wrong?

thanks!

the problem here loading dplyr first , plyr, plyr's function summarise masking dplyr's function summarise. when happens warning:

require(plyr)     loading required package: plyr ------------------------------------------------------------------------------------------ have loaded plyr after dplyr - cause problems. if need functions both plyr , dplyr, please load plyr first, dplyr: library(plyr); library(dplyr) ------------------------------------------------------------------------------------------  attaching package: ‘plyr’  following objects masked ‘package:dplyr’:      arrange, desc, failwith, id, mutate, summarise, summarize 

so in order code work, either detach plyr detach(package:plyr) or restart r , load plyr first , dplyr (or load dplyr):

library(dplyr) dfx %>% group_by(group, sex) %>%    summarise(mean = round(mean(age), 2), sd = round(sd(age), 2)) source: local data frame [6 x 4] groups: group    group sex  mean    sd 1       f 41.51  8.24 2       m 32.23 11.85 3     b   f 38.79 11.93 4     b   m 31.00  7.92 5     c   f 24.97  7.46 6     c   m 36.17  9.11 

or can explicitly call dplyr's summarise in code, right function called no matter how load packages:

dfx %>% group_by(group, sex) %>%    dplyr::summarise(mean = round(mean(age), 2), sd = round(sd(age), 2))