使用两个数据帧执行条件（aka查找）功能？

Question

I'm hoping someone can help me with this challenge (I'm fairly new to R). I have one data frame (Plots) that has unique records for tree species (Spp) and tree size (Dbh). I have a second data frame (Parameters) that gives parameters (X and Y) for a function for each species.

Plots
Id  Spp Dbh
414 SM  27.2
415 BE  17.4
416 YB  35.8
418 SM  43.5
419 SM  53.3
420 SM  53.3
421 SM  11.9
422 TL  27.5
423 XS  13.2

Parameters
Species X   Y
BE  1   10
SM  2   20
YB  3   30
OTH 4   40

I need look at every record of Plots$Spp and perform a simple function on Plots$Dbh using the X and Y records from Parameters (ie X * Dbh^Y ) for the corresponding Species . If Plots$Spp has a record that is not in Parameters$Species (ie XS or TL), I need to use the X and Y values for OTH.

I first tried using merge() but couldn't get it to work with the XS/OTH situation. I also tried a for loop with nested if/else if/else, but again I failed. Any help would be appreciated!

Answer 1

Perhaps this approach:

library(tidyverse)

Plots %>%
  mutate(Species = ifelse(Spp %in% Parameters$Species, Spp, "OTH")) %>%
  left_join(Parameters)

create a new variable "Species" in Plots data frame by first checking if Plots$Spp is in Parameters$Species if yes leave Spp , if not replace with "OTH" and then join the resulting data frame with Parameters by "Species" column.

#output
   Id Spp  Dbh Species X  Y
1 414  SM 27.2      SM 2 20
2 415  BE 17.4      BE 1 10
3 416  YB 35.8      YB 3 30
4 418  SM 43.5      SM 2 20
5 419  SM 53.3      SM 2 20
6 420  SM 53.3      SM 2 20
7 421  SM 11.9      SM 2 20
8 422  TL 27.5     OTH 4 40
9 423  XS 13.2     OTH 4 40

data:

Plots <- read.table(text = "Id  Spp Dbh
414 SM  27.2
415 BE  17.4
416 YB  35.8
418 SM  43.5
419 SM  53.3
420 SM  53.3
421 SM  11.9
422 TL  27.5
423 XS  13.2", header = T, stringsAsFactors = FALSE)

Parameters <- read.table(text = "Species X   Y
BE  1   10
SM  2   20
YB  3   30
OTH 4   40", header = T, stringsAsFactors = FALSE)