How to get value of last non-NA column [duplicate]

A bit difficult to explain, but I have a dataframe with values that look like a staircase - for every date, there are different columns that have NA for some dates. I want to create a new column that has the last non-NA column value in it.

Hopefuly it makes more sense with this example:

Sample dataframe:

test <- data.frame("date" = c(as.Date("2020-01-01"), as.Date("2020-01-02"), as.Date("2020-01-03")),
                   "a" = c(4, 3, 4),
                   "b" = c(NA, 2, 1),
                   "c" = c(NA, NA, 5))

Desired output:

date............val
2020-01-01...... 4
2020-01-02...... 2
2020-01-03...... 5

I'd also prefer not to do something like take the row number of the date and take that column number + 1, but if that's the only way to do it, that's that. Thanks!

Asked By: Kathy
||

Answer #1:

You can use max.col with ties.method set as "last" to get last non-NA value in each row.

test$val <- test[cbind(1:nrow(test), max.col(!is.na(test), ties.method = 'last'))]
test

#        date a  b  c val
#1 2020-01-01 4 NA NA   4
#2 2020-01-02 3  2 NA   2
#3 2020-01-03 4  1  5   5
Answered By: Ronak Shah

Answer #2:

Here's a Tidyverse-based approach - convert the columns to rows using pivot_longer, then get the last row where the value isn't NA for each date:

library(dplyr)
library(tidyr)

test %>% 
    pivot_longer(-date) %>% 
    filter(!is.na(value)) %>% 
    group_by(date) %>% 
    summarize(value = tail(value, 1), .groups = "drop")
Answered By: tfehring

Answer #3:

You can also do this with dplyr's coalesce function, which takes the first non-missing element from the provided vectors.

library(dplyr)

test %>%
  mutate(val = coalesce(c, b, a))
#>         date a  b  c val
#> 1 2020-01-01 4 NA NA   4
#> 2 2020-01-02 3  2 NA   2
#> 3 2020-01-03 4  1  5   5

Created on 2020-07-07 by the reprex package (v0.3.0)

Note that if you have many columns, @tfehring & @Ronak's solutions will be better suited, as for this method you'll have to manually specify your columns. It does have the benefit of being short & sweet, though.

Answered By: RyanFrost
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