Rowwise median for multiple columns using dplyr

Question

Given the following dataset, I want to compute for each row the median of the columns M1,M2 and M3. I am looking for a solution where the final column is added to the datafr

Answer 1

We could use rowMedians

library(matrixStats)
library(dplyr)
df %>% 
    mutate(Median = rowMedians(as.matrix(.[grep('M\\d+', names(.))])))

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Or if we need to use only tidyverse functions, convert it to 'long' format with gather, summarize by row and get the median of the 'value' column

df %>% 
    rownames_to_column('rn') %>%
    gather(key, value, starts_with('M')) %>%
    group_by(rn) %>% 
    summarise(Median = median(value)) %>%
    ungroup %>% 
    select(-rn) %>%
    bind_cols(df, .)

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Or another option is rowwise() from dplyr (hope the row is not a problem)

df %>% 
   rowwise() %>% 
   mutate(Median =  median(c(!!! rlang::syms(grep('M', names(.), value=TRUE)))))