R：如何以编程方式遍历拆分的数据帧

Question

I have data set where data for a series of lots is stored sequentially down a column, and multiple parameters are given for each lot (also sequentially). The file looks something like this:

LotID,Param,Nominal,Value
R0001,Len,1.2500,1.234
R0001,Dia,2.0000,1.979
R0002,Len,1.2500,1.252
R0002,Dia,2.0000,2.010

I'm able to drill down to the data I need by importing it into a data frame, splitting the data frame by LotID, and then splitting again by Param, which is great. Here is the code I am using for that:

myCapFull <- read.csv("capabilityFull.csv")
myCapSplit <- split(myCapFull, myCapFull$LotID)
myR0001 <- split(myCapSplit$R0001,myCapSplit$R0001$Param)
myR0001$Dia$Value # Returns 1.979

But what I want to do is use iter to iterate over each parameter of each lot, and I can't find a way to do that programmatically. I know how to write the code if I know all of the names in the LotID field, but that doesn't help inside a for/next loop. I have a feeling that I'm just missing one very simple command, and I've spent a lot of time searching but haven't found the answer. I'm new to R, this is really my first real-world application of it, so any help would be much appreciated.

Answer 1

If you don't know the values in LotID , you can access the data frames in your list with numeric indices:

> myCapSplit[[1]]
  LotID Param Nominal Value
1 R0001   Len    1.25 1.234
2 R0001   Dia    2.00 1.979
> 
> myCapSplit[[2]]
  LotID Param Nominal Value
3 R0002   Len    1.25 1.252
4 R0002   Dia    2.00 2.010

Answer 2

Maybe you're looking for subset ?

subset(myCapFull, Param=="Dia" & LotID == "R0001")
#   LotID Param Nominal Value
# 2 R0001   Dia       2 1.979    

Alternatively, you can look into documentation for [.data.frame for more info on how to subset, or into data.table , dplyr , or plyr packages for manipulation of data frames by groups (ie split apply combine analysis ). For example, here we find the mean of each parameter across all lots with data.table :

library(data.table)
DT <- data.table(myCapFull)
DT[, mean(Value), by=Param]
#    Param     V1
# 1:   Len 1.2430
# 2:   Dia 1.9945