question on lag.zoo

Hi Guys,

I'm using zoo package now.  I found lag is not doing what I assumed.

x <- zoo(11:21)
z <- zoo(1:10, yearqtr(seq(1959.25, 1961.5, by = 0.25)), frequency = 4)
x

 1  2  3  4  5  6  7  8  9 10 11
11 12 13 14 15 16 17 18 19 20 21

lag(x)

 1  2  3  4  5  6  7  8  9 10
12 13 14 15 16 17 18 19 20 21

z

1959 Q2 1959 Q3 1959 Q4 1960 Q1 1960 Q2 1960 Q3 1960 Q4 1961 Q1 1961 Q2 1961 Q3
     1       2       3       4       5       6       7       8       9      10

lag(z)

1959 Q1 1959 Q2 1959 Q3 1959 Q4 1960 Q1 1960 Q2 1960 Q3 1960 Q4 1961 Q1 1961 Q2
     1       2       3       4       5       6       7       8       9      10


Why z and lag (z) are of same length while lag(x) is shorter by one than x?

I assume lag(z) would give me like this:
1959 Q3 1959 Q4 1960 Q1 1960 Q2 1960 Q3 1960 Q4 1961 Q1 1961 Q2 1961 Q3
 2       3       4       5       6       7       8       9      10
ie preserve the relationship between timestamp and the value.

Same things applies to lag(x) but I guess both make sense:
 1  2  3  4  5  6  7  8  9 10

12 13 14 15 16 17 18 19 20 21
or
 2  3  4  5  6  7  8  9 10 11

12 13 14 15 16 17 18 19 20 21


Any insight?

Cheers,

Bo

Its a FAQ.  x is of class "zoo" but z is of class "zooreg" so one is using

zoo.lag and the is using zooreg.lag.  See question #6 in the zoo FAQ:
  vignette("zoo-faq")
and also
  ?lag.zoo


On Sun, Mar 2, 2008 at 9:12 AM, Bo Zhou <bozhou1981 at hotmail.com> wrote:

Hi Guys,

I'm using zoo package now.  I found lag is not doing what I assumed.

x <- zoo(11:21)
z <- zoo(1:10, yearqtr(seq(1959.25, 1961.5, by = 0.25)), frequency = 4)
x

 1  2  3  4  5  6  7  8  9 10 11
11 12 13 14 15 16 17 18 19 20 21

lag(x)

 1  2  3  4  5  6  7  8  9 10
12 13 14 15 16 17 18 19 20 21

z

1959 Q2 1959 Q3 1959 Q4 1960 Q1 1960 Q2 1960 Q3 1960 Q4 1961 Q1 1961 Q2 1961 Q3
     1       2       3       4       5       6       7       8       9      10

lag(z)

1959 Q1 1959 Q2 1959 Q3 1959 Q4 1960 Q1 1960 Q2 1960 Q3 1960 Q4 1961 Q1 1961 Q2
     1       2       3       4       5       6       7       8       9      10


Why z and lag (z) are of same length while lag(x) is shorter by one than x?

I assume lag(z) would give me like this:
1959 Q3 1959 Q4 1960 Q1 1960 Q2 1960 Q3 1960 Q4 1961 Q1 1961 Q2 1961 Q3
 2       3       4       5       6       7       8       9      10
ie preserve the relationship between timestamp and the value.

Same things applies to lag(x) but I guess both make sense:
 1  2  3  4  5  6  7  8  9 10

12 13 14 15 16 17 18 19 20 21
or
 2  3  4  5  6  7  8  9 10 11

12 13 14 15 16 17 18 19 20 21


Any insight?

Cheers,

Bo