Simple function to find maximum value up to each position in an array?

Question

Suppose we have the following data frame and we wish to find the maximum of column 'value' up to each row, i.e. the resulting new column should be c(4993, 4993, 5036, 5036, 5036). Of course I can write a loop for this, but just wondering is there a simple dplyr solution as loops can get tedious to read?

> myDf[1:5, ]
        time value
1 2018-01-03  4993
2 2018-01-15    52
3 2018-08-02  5036
4 2018-08-17  -162
5 2018-09-05  4806

Many thanks!

The `cummax` function is built in for this purpose. – MrFlick Aug 31 '20 at 02:10 — MrFlick, Aug 31 '20 at 02:10

score 1 · Answer 1 · answered Aug 31 '20 at 02:10

You might be looking for the built-in function cummax:

set.seed(641032)
x <- rnorm(10)
x
#>  [1]  0.91326263  1.29385203  1.39573077  0.02985411  0.11766056 -1.15891724
#>  [7] -1.02509101 -0.31448858 -0.06675214 -1.34341847
cummax(x)
#>  [1] 0.9132626 1.2938520 1.3957308 1.3957308 1.3957308 1.3957308 1.3957308
#>  [8] 1.3957308 1.3957308 1.3957308

Simple function to find maximum value up to each position in an array?

1 Answers1