Mutate multiple / consecutive columns (with dplyr or base R)

Question

I\'m trying to create \"waves\" of variables that represent repeated measures. Specifically, I\'m trying to create consecutive variables that represent the mean values for

Answer 1

Here is one way with the package zoo:

library(zoo)
t(rollapply(t(df), width = 10, by = 10, function(x) sum(x)/10))

Here is one way to do it with base R:

splits <- 1:100
dim(splits) <- c(10, 10)
splits <- split(splits, col(splits))
results <- do.call("cbind", lapply(splits, function(x) data.frame(rowSums(df[,x] / 10))))
names(results) <- paste0("wave_", 1:10)
results

Another very succinct way with base R (courtesy of G.Grothendieck):

t(apply(df, 1, tapply, gl(10, 10), mean))

And here is a solution with dplyr and tidyr:

library(dplyr)
library(tidyr)
df$row <- 1:nrow(df)
df2 <- df %>% gather(column, value, -row)
df2$column <- cut(as.numeric(gsub("X", "", df2$column)),breaks = c(0:10*10))
df2 <- df2 %>% group_by(row, column) %>% summarise(value = sum(value)/10)
df2 %>% spread(column, value) %>% select(-row)