How can I calculate multiple mean values for time series within a dataframe in R?

Question

I am quite new to R and struggling with the following issue:

        Country.Name variable Quantity
    1         World     1977  2524966
    2         World     1978  2552326
    3         World     1979  2710504
    4         World     1980  2732926
    5         World     1981  2636113
    6         World     1982  2803907
    7         World     1983  2778356
    8         World     1984  2693296
    9         World     1985  2695397
    10        World     1986  2747397
    (...)
    30        World     2006  3100186

For df$Quantity (numeric) I want to calculate two separate means, from (1) 1977 to 1991 and from (2) 1992 to 2006. Further search hasn't helped me solve that issue, so I'd be glad to hear if anyone could help me out with this!

Best, Jannis

Welcome to StackOverflow! Please read the info about [how to ask a good question](http://stackoverflow.com/help/how-to-ask) and how to give a [reproducible example](http://stackoverflow.com/questions/5963269). This will make it much easier for others to help you. — Sotos, Nov 07 '18 at 10:08
Here is an `aggregate` to get you started, `aggregate(Quantity ~ with(df, ifelse(variable >= 1977 & variable <= 1991, 1, 2)), df, mean)` — Sotos, Nov 07 '18 at 10:15
`aggregate(Quantity ~ (variable <= 1991), data=df, FUN=mean)` — jogo, Nov 07 '18 at 10:22

score 1 · Accepted Answer · answered Nov 07 '18 at 10:15

Here is a base R option:

aggregate(df$Quantity,
    by=list(ifelse(df$variable >= 1977 & df$variable <= 1991, 0, 1)),
    FUN=mean)

This buckets rows from 1977 to 1991 (inclusive on both ends) into a zero bucket, and all others years into a 1 bucket. Then, aggregate finds the mean for all rows belonging to both buckets.

How can I calculate multiple mean values for time series within a dataframe in R?

1 Answers1