CODEWITHSUNDEEP
rdplyrreshape2
Gregory
Gregory

Reputation: 4279

How to reshape2 and summarize a data frame?

I need to reshape and summarize a data frame. I've identified reshape2 (and perhaps dplyr) as the most likely package to do the job, but the only approach I've come up with is so inefficient and tedious that it doesn't bear presenting here. Here's an example data set; the real one has more variables to summarize with more aggregate functions:

> d <- data.frame(type=sample(c("dog","goat", "pika"), 50, replace=TRUE), a=rnorm(50, 50,8), b=rnorm(50,70,4))

> head(d)
  type        a        b
1  dog 49.29015 73.09723
2  dog 35.16051 72.44976
3  dog 58.37524 66.41876
4 goat 66.05670 64.05190
5 goat 51.45586 69.84018
6 goat 63.10084 69.70595

I'm trying to get it into a shape like this:

  type variable mean sd
1  dog  a        50   8
2  dog  b        70   4
3  goat a        50   8
4  goat b        70   4
5  pika a        50   8
6  pika b        70   4

Upvotes: 1

Views: 699

Answers (2)

akrun
akrun

Reputation: 887881

You could use dplyr with tidyr

 library(dplyr)
 library(tidyr)
 d %>% 
   gather(variable, val, a:b) %>% 
   group_by(type, variable) %>%
   summarise(Mean=mean(val, na.rm=TRUE), Sd=sd(val, na.rm=TRUE))

gives the result (it is different because the example didn't used set.seed

 #  type variable     Mean       Sd
 #1  dog        a 45.72271 7.304119
 #2  dog        b 72.16658 5.562985
 #3 goat        a 48.10097 6.856664
 #4 goat        b 70.16296 4.014350
 #5 pika        a 52.88040 6.434812
 #6 pika        b 68.70830 4.343295

Upvotes: 4

MrFlick
MrFlick

Reputation: 206546

This uses reshape2 and dplyr

library(reshape2)
library(dplyr)
summarize(group_by(melt(d), type, variable), mean=mean(value), sd=sd(value))

# Source: local data frame [6 x 4]
# Groups: type

#   type variable     mean        sd
# 1  dog        a 47.42249 10.669676
# 2  dog        b 68.92475  3.659657
# 3 goat        a 52.41433  7.181254
# 4 goat        b 70.28015  3.815483
# 5 pika        a 51.78442  8.513349
# 6 pika        b 71.10006  4.445932

Upvotes: 4

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