Q:

Attributes in `data.frame` for use in `seas` package

I’m learning R and am trying to use the package seas to apply to my own data.  However, I am having some issues with my input data. 
The package provides an example data.frame with the following structure:
stopifnot(packageVersion("seas") >= '0.4.3') #ensure most recent loaded
str(mscdata)
data.frame':    26358 obs.  of  10 variables:
 $ id    : Factor w/ 3 levels "1096450","1108447",..: 1 1 1 1 1 1 1 1 1 1 ...
 $ year  : int  1975 1975 1975 1975 1975 1975 1975 1975 1975 1975 ...
 $ yday  : int  1 2 3 4 5 6 7 8 9 10 ...
 $ date  : Date, format: "1975-01-01" "1975-01-02" ...
 $ t_max : atomic  1.1 0.6 0.6 -4.4 -0.6 -1.1 -7.2 -7.8 -25.6 -26.7 ...
  ..- attr(*, "units")= chr "°C"
  ..- attr(*, "long.name")= chr "daily maximum temperature"
 $ t_min : atomic  -7.2 -7.2 -7.2 -10 -6.1 -10.6 -13.3 -27.2 -32.8 -38.3 ...
  ..- attr(*, "units")= chr "°C"
  ..- attr(*, "long.name")= chr "daily minimum temperature"
 .....

The structure of my data.frame appears like this:
str(dat0)
data.frame':    27029 obs.  of  6 variables:
 $ id    : Factor w/ 1 level "2228551": 1 1 1 1 1 1 1 1 1 1 ....
 $ year  : int  1940 1940 1940 1940 1940 1940 1940 1940 1940 1940 ...
 $ date  : Date, format: "1940-01-01" "1940-01-02" ...
 $ t_max : num  -21.1 -17.2 -15 -16.1 -13.9 -16.1 -15.6 -14.4 -17.2 -25 ...
 $ t_min : num  -32.8 -24.4 -18.9 -17.8 -17.8 -24.4 -19.4 -21.1 -24.4 -29.4  
.....

Note when I load the first data.frame from the package and compare it with my data.frame, they have the same column headings (colnames), as follows:
colnames(mscdata)
[1] "id"     "year"   "yday"   "date"   "t_max"  "t_min"  "t_mean" "rain"  
[9] "snow"   "precip"

My question is: how can I edit the data structure of my data.frame to match the format of package:seas (e.g. t_min has two attr, while mine has only one)

A:

Hopefully you will be able to generalize from this:
library(seas)
data(mscdata)
str(mscdata)
### similar to example given above
dat0 <- data.frame(
    year=rep(1940, 10),
    t_max=c(21.1, -17.2, -15, -16.1, -13.9, -16.1, -15.6, -14.4, -17.2, -25),
    t_min=c(-32.8, -24.4, -18.9, -17.8, -17.8, -24.4, -19.4, -21.1, -24.4, -29.4)
    )
attr(dat0$t_max, "long.name") <- "daily maximum temperature"
###  or copy directly from example
attr(dat0$t_max, "units") <- attr(mscdata$t_max, "units")

Or simply:
attributes(dat0$t_max) <- attributes(mscdata$t_max)

See ? attr or ? attributes for more.