创建一个表，其中包含每年的平均持续时间和类型

Question

我有以下数据框架:

library("lubridate")
df = data.frame(c("AAA","BBB","AAA"),
                c("2012","2013","2012"),
                c("2012-12-30 08:01:01","2013-12-30 09:05:02","2012-12-30 08:08:01"),
                c("2012-12-30 09:01:00","2013-12-30 10:15:00","2012-12-30 08:11:01"))
colnames(df) = c("type","year","start","end")
df$duration = difftime(ymd_hms(df$end), ymd_hms(df$start),units="mins")

现在我想创建一个平均持续时间表，它看起来如下:

     2012   2013
AAA  31.49  0.00
BBB  0.00   69.97

我应该使用哪些函数来创建这样的表?

更新:

这就是我所尝试的，但是我如何添加year ?:

mean_duration_per_type_year = aggregate(duration~type,
                                        data=df,
                                        mean)

Answer 1

使用reshape2包可以这样做:

library(reshape2)
temp <- aggregate(df$duration, by = list(type = df$type, year = df$year), mean)
final <- dcast(temp, type~year)
final[is.na(final)] <- 0 # optional : replace the NA values with 0

final
#   type     2012     2013
# 1  AAA 31.49167  0.00000
# 2  BBB  0.00000 69.96667

注意，如果您希望类型是行名，您可以添加以下行:

rownames(final) <- final$type
final$type <- NULL
final
#         2012     2013
# AAA 31.49167  0.00000
# BBB  0.00000 69.96667