want to apply zero in total for missing time in table a

Question

> a
    deptime total
1        NA   341
2         1     2
3         4     1
4         5     1
5         6     1
6         8     1
7         9     2
8        10     1
9        11     1
10       15     2
11       17     2
12       20     1
13       21     2
14       23     1
15       25     3
16       28     1
17       29     5
18       30     2
19       31     1
20       33     1
21       36     2
22       38     1
23       39     2
24       41     1
25       44     2
26       45     2
27       50     1
28       51     2
29       52     2
30       54     1
31       57     1
32       58     1
33      103     1
34      104     1
35      105     1
36      107     1
37      114     1
38      119     1
39      126     1
40      131     1
41      136     1
42      148     1
43      158     1
44      208     1
45      230     1
46      244     1
47      410     1
48      418     1
49      441     1
50      446     1
51      452     2
52      455     2
53      456     1
54      500     3
55      501     1
56      505     1
57      507     1
58      508     1
59      511     1
60      515     2
61      516     2
62      517     1
63      518     3
64      519     2
65      520     4

Answer 1

1) The zoo package has na.fill for this purpose. It is non-destructive:

library(zoo)
a0 <- na.fill(a, fill = 0) # replace NAs in all columns

or if you only want to fill the first column:

a$deptime <- na.fill(a$deptime, fill = 0)

2) Without zoo:

a[is.na(a)] <- 0 # replace NAs in all columns

or just the deptime column:

a$deptime[is.na(a$deptime)] <- 0

This also just does the replacement in the deptime column and is non-destructive:

a0 <- transform(a, deptime = replace(deptime, is.na(deptime), 0))

Answer 2

a[1,"deptime"] <- 0

or

a[is.na(a$deptime),]$deptime <- 0

or many other variants of these