Calculating ratios by group with dplyr

Question

Using the following dataframe I would like to group the data by replicate and group and then calculate a ratio of treatment values to control values.

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Answer 1

You can try:

group_by(dataIn, replicate) %>% 
    summarise(ratio = quant[group=="case"]/quant[group=="controls"])
#Source: local data frame [4 x 2]
#
#  replicate    ratio
#1      four 1.078562
#2       one 1.333333
#3     three 1.070573
#4       two 1.446449

Because you grouped by replicate and group, you could not access data from different groups at the same time.