Geoff,
I'm not exactly sure what you're trying to do, but if you want to match up
information in two data frames according to a common column in each (node
in map and Bus in period), then the merge() function might do the trick
for you. Look at the examples in
?merge
Jean
Geoff Leyland <geoff_leyl...@fastmail.fm> wrote on 06/11/2012 09:27:39 PM:
> Hi, I'm new here,
>
> I'd like to map a set of values in a data frame to another set of
> values in another frame (think a c++ map<>, a python dict or a hash
lookup)
>
> Specifically, I have a data frame of information about trading
> periods in the NZ electricity market. For each period I have
> information about each bus (or node) in the network. I'd like add a
> "column" to the data frame containing the island that the bus is on.
>
> I'm afraid my success at searching for an answer is restricted by
> not knowing what this operation might be called in R, but I found a
> something on stackoverflow [1] and tried the following:
>
> map <- read.table("../node_islands.csv", header=TRUE, sep=",")
> map <- setNames(map$island, map$node)
> periods$Island = map[periods$Bus]
>
> Where after the first line, but before the second and third:
>
> > map[1:3,]
> node island
> 1 ABY0111 SI
> 2 ABY1101 SI
> 3 ADD0111 SI
>
> and:
>
> > periods[1:3, c("Date", "Period", "Bus", "Price")]
> Date Period Bus Price
> 1 2004-01-01 1 ABY0111 31.20
> 2 2004-01-01 1 ADD0111 32.43
> 3 2004-01-01 1 ADD0661 32.38
>
> This seems to work (it fooled me for quite a while :-) ), but the
> following check:
>
> for (b in periods$Bus)
> {
> if (periods[periods$Bus == b, "Island"] != map[b])
> {
> print(b)
> print(periods[periods$Bus == b, "Island"][1:1])
> print(map[b])
> }
> }
>
> prints a number of lines where periods$Island does not match the
> corresponding value in map:
>
> [1] "ALB0331"
> [1] SI
> Levels: NI SI
> ALB0331
> NI
> Levels: NI SI
> [1] "APS0111"
> [1] NI
> ...
>
> Clearly, I've missed the point here. Would anyone be so kind as
> help me find it or suggest which FM I might need to R?
>
> Cheers,
> Geoff
>
> [1] http://stackoverflow.com/questions/7547597/dictionary-style-
> replace-multiple-items-in-r
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