Fill in data frame with values from rows above

Question

Say I have a data frame like this:

ID,  ID_2, FIRST, VALUE
-----------------------
\'a\', \'aa\', TRUE, 2
\'a\', \'ab\', FALSE, NA
\'a\', \'ac\', FALSE, NA
\         


        

Answer 1

If the VALUE for a specific ID always appears in the first record, which seems to be the case for your data, you can use match to find that record:

df <- read.csv(textConnection("

ID,  ID_2, FIRST, VALUE
'a', 'aa', TRUE, 2
'a', 'ab', FALSE, NA
'a', 'ac', FALSE, NA
'b', 'aa', TRUE, 5
'b', 'ab', FALSE, NA

"))

df$VALUE <- df$VALUE[match(df$ID, df$ID)]
df
#    ID  ID_2  FIRST VALUE
# 1 'a'  'aa'   TRUE     2
# 2 'a'  'ab'  FALSE     2
# 3 'a'  'ac'  FALSE     2
# 4 'b'  'aa'   TRUE     5
# 5 'b'  'ab'  FALSE     5