Subtract last value observed minus starting value divided by number of cells in row in R

user_12055305 0
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Hi everyone i have this problem, i want to susbstract the last value of observed in a row with the starting value and divide it by the number of cells with values present for example:

 Day1 day2 day3 day4 day5
3    2     1    1    1
3    4     NA   NA   NA
5    6     7    NA   NA
7    8     9    10   12

For: First one the value is (1-3)/5 Second one the value is (4-3)/2 Third one the value is (7-5)/3 Fourth one the value is (12-7)/5

And save all values in a new column

dataframe r
2 Answers

1) Define stat function and then apply it by row.

library(dplyr)

stat <- function(x) (tail(x, 1) - head(x, 1)) / length(x)

DF %>% 
  rowwise %>%
  mutate(stat = stat(na.omit(c_across()))) %>%
  ungroup

giving:

# A tibble: 4 x 6
   Day1  day2  day3  day4  day5   stat
  <int> <int> <int> <int> <int>  <dbl>
1     3     2     1     1     1 -0.4  
2     3     4    NA    NA    NA  0.5  
3     5     6     7    NA    NA  0.667
4     7     8     9    10    12  1

2) Base R or using base R and stat from above:

cbind(DF, stat = apply(DF, 1, function(x) stat(na.omit(x))))
user_5165480

One way of doing it is by identifying the maximum non-NA index in each row.
Using apply:

dtf = read.table(header = TRUE, 
                 text = ' Day1 day2 day3 day4 day5
                          3    2     1    1    1
                          3    4     NA   NA   NA
                          5    6     7    NA   NA
                          7    8     9    10   12')
                
dtf$ratio = apply(dtf, 1, function(x){ind_last = max(which(!is.na(x)
                                      (x[ind_last] - x[1]) / ind_last})

It leads to:

  Day1 day2 day3 day4 day5      ratio
  1    3    2    1    1    1 -0.4000000
  2    3    4   NA   NA   NA  0.5000000
  3    5    6    7   NA   NA  0.6666667
  4    7    8    9   10   12  1.0000000
user_117136830
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