How to divide every value with the maximum value in each element in list object

Question

I have data in xts format. Data consists of 360 monthly observations of 650 stocks. I spilt the data into years which results in a large list object with 30 elements (1 for each year) in it. Now for each stock value in every element in the list, I want to divide the value by the maximum value in the year, i.e. I have a stock in tata motor I want to divide its each 2005 year value by the maximum value in the 2005. I am replicating this the following code. I have divide the data into years. But not able to do further.

library(xts)
library(zoo)
library(PerformanceAnalytics)
## splitting the data into years
managers_years<-split(managers,f="years")

Answer 1

The problem can also be solved with out converting into data frame. With help of apply family functions, one can solve this. Try following code

test<-lapply(managers_years,apply,2,function(x)x/max(x))

Answer 2

For each object, convert it to a data.frame. Apply the transformation over all columns and convert it back to zoo.

• map applies a function to all the objects.
• fortify.zoo converts the zoo object to a data.frame with an Index column.
• mutate_at applies a function over multiple columns.
• read.zoo converts the data.frame back to zoo.

map(
  managers_years,
  function(df) {
    df %>%
    fortify.zoo() %>%
    mutate_at(vars(-Index), ~. / max(., na.rm = TRUE)) %>%
    read.zoo()
  }
)

mutate_at can be replaced with the more recent across syntax.

map(
  managers_years,
  function(df) {
    df %>%
      fortify.zoo() %>%
      mutate(across(-Index, ~. / max(., na.rm = TRUE))) %>%
      read.zoo()
  }
)