Average data by month for a given latitude and longitude? - r

Question

I have a table with the following headers and example data
Lat Long Date Value.
30.497478 -87.880258 01/01/2016 10
30.497478 -87.880258 01/02/2016 15
30.497478 -87.880258 01/05/2016 20
33.284928 -85.803608 01/02/2016 10
33.284928 -85.803608 01/03/2016 15
33.284928 -85.803608 01/05/2016 20
I would like to average the value column on monthly basis for a particular location.
So example output would be
Lat Long Month Avg Value
30.497478 -87.880258 January 15

Answer 1

A solution using dplyr and lubridate.
library(dplyr)
library(lubridate)
dt2 <- dt %>%
mutate(Date = mdy(Date), Month = month(Date)) %>%
group_by(Lat, Long, Month) %>%
summarise(`Avg Value` = mean(Value))
dt2
# A tibble: 2 x 4
# Groups: Lat, Long [?]
Lat Long Month `Avg Value`
<dbl> <dbl> <dbl> <dbl>
1 30.49748 -87.88026 1 15
2 33.28493 -85.80361 1 15

Answer 2

You can try the following, but it first modifies the data frame adding an extra column, Month, using package zoo.
library(zoo)
dat$Month <- as.yearmon(as.Date(dat$Date, "%m/%d/%Y"))
aggregate(Value. ~ Lat + Long + Month, dat, mean)
# Lat Long Month Value.
#1 30.49748 -87.88026 jan 2016 15
#2 33.28493 -85.80361 jan 2016 15
If you don't want to change the original data, make a copy dat2 <- dat and change the copy.
DATA
dat <-
structure(list(Lat = c(30.497478, 30.497478, 30.497478, 33.284928,
33.284928, 33.284928), Long = c(-87.880258, -87.880258, -87.880258,
-85.803608, -85.803608, -85.803608), Date = structure(c(1L, 2L,
4L, 2L, 3L, 4L), .Label = c("01/01/2016", "01/02/2016", "01/03/2016",
"01/05/2016"), class = "factor"), Value. = c(10L, 15L, 20L, 10L,
15L, 20L)), .Names = c("Lat", "Long", "Date", "Value."), class = "data.frame", row.names = c(NA,
-6L))
EDIT.
If you want to compute several statistics, you can define a function that computes them and returns a named vector and call it in aggregate, like the following.
stat <- function(x){
c(Mean = mean(x), Median = median(x), SD = sd(x))
}
agg <- aggregate(Value. ~ Lat + Long + Month, dat, stat)
agg <- cbind(agg[1:3], as.data.frame(agg[[4]]))
agg
# Lat Long Month Mean Median SD
#1 30.49748 -87.88026 jan 2016 15 15 5
#2 33.28493 -85.80361 jan 2016 15 15 5