subset data frame in R using loop

问题

I have a data frame that looks like this:

----------

index   ID   date              Amount
2       1001 2010-06-08         0
21      1001 2010-10-08        10
6       1002 2010-08-16        30
5       1002 2010-11-25        20
9       1003 2010-01-01         0
8       1003 2011-03-06        10
12      1004 2012-03-12        10
11      1004 2012-06-21        10
15      1005 2010-01-01        30
13      1005 2010-04-06        20

I want to subset this data so that i have new data frames, one for each ID like this

index   ID   date              Amount
2       1001 2010-06-08         0
21      1001 2010-10-08        10

and

6       1002 2010-08-16        30
5       1002 2010-11-25        20

and so on.

I dont need to save the new data frames, but use it to perform some basic calculations. Also i want to do this on my entire table consisting of more than 10000 IDs and hence the need for a loop. I tried this

    temp <- data.frame(Numb=c(),Dt=c(),Amt=c())
for (i in seq_along(stNew$ID)){
   temp[i,] <- subset(stNew, stNew[i,]==stNew$ID[i])
}

but that didnt work. Any suggestions? Thanks.

回答1:

may be like this

    IDs<-unique(df$ID)
    for (i in 1:length(IDs)){ 
    temp <- df[df$ID==IDs[i],]
    #more things to do with temp
    }

回答2:

Take a look at the list2env and split function. Hereby some examples using the iris dataset.

two way:

list_df <- split(iris, iris$Species) #split the dataset into a list of datasets based on the value of iris$Species
list2env(list_DF, envir= .GlobalEnv) #split the list into separate datasets

one way:

list2env(split(iris, iris$Species), envir = .GlobalEnv)

Or you can assign custom names for the new datasets with a for loop:

iris_split <- split(iris, iris$Species)
new_names <- c("one", "two", "three")
for (i in 1:length(iris_split)) {
  assign(new_names[i], iris_split[[i]])
}

updates with examples

Related post

回答3:

    iris_split <- split(iris, iris$Species)

Dynamically you can assign the data.frame name

    new_names <- as.character(unique(iris$Species))

    for (i in 1:length(iris_split)) {
    assign(new_names[i], iris_split[[i]])
    }

来源：https://stackoverflow.com/questions/19882085/subset-data-frame-in-r-using-loop