Colomn median for each five elements of a column Using a dataframe-CodePudding

I have a dataframe with 20 Columns and 20 rows. I want to calculate the median of each five row for each Column Using a loop or a function. I need 20 columns with five median for each of them.

CodePudding user response：

library(dplyr)
set.seed(1)
matrix(rexp(400, rate=.1), ncol=20) %>% 
    as_tibble(.name_repair = ~paste0('X', 1:20)) %>%
    group_by(id = rep(1:4, each = 5)) %>%
    summarise(
        across(everything(), median)
    )
# A tibble: 4 x 21
     id    X1    X2    X3    X4    X5    X6    X7    X8    X9   X10   X11   X12   X13   X14   X15   X16   X17   X18   X19    X20
  <int> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>  <dbl>
1     1  4.36  5.66 10.8  11.1   8.19  5.16  7.43 10.3  14.8   7.51  6.75 10.9  13.2   7.37  6.92 17.8   4.63  9.56  7.17  5.03 
2     2  9.57  9.97  9.95  8.37 13.5   7.63 11.9   8.05 21.1   5.42  6.73  6.22  4.79 10.1   4.33 12.8   6.55  5.00  7.61  3.43 
3     3 12.4   3.24  5.95 17.8   6.81 14.2   3.79 17.4  12.9   8.02 10.3   5.62  7.22  5.21  2.92  2.65  6.85  4.29  5.85  0.542
4     4  6.55  7.25  7.74  8.15  2.64  2.99  7.85  7.12  7.62  7.37  6.63  6.46  7.50 12.9  10.9   6.59  1.93 10.5   4.68 11.4

CodePudding user response：

In base R you could accomplish the same by using tapply:

set.seed(1)
m <- matrix(rexp(400, rate=.1), ncol=20)
t(tapply(m, list(col(m), (row(m)-1) %/% 5), median))

          1        2         3         4         5         6         7
0  4.360686 5.658655 10.798811 11.081767  8.185142  5.162061  7.430436   ...
1  9.565675 9.968130  9.945558  8.370065 13.456440  7.631800 11.910946   ...
2 12.376036 3.240102  5.946177 17.847654  6.812291 14.195492  3.788268   ...
3  6.547466 7.252143  7.741878  8.145358  2.637383  2.991589  7.851209   ...