Create list in R with specific iteration

问题

I have a folder with 10 files that I import in R as S

S<-list.files(S1_path, recursive = TRUE, full.names = TRUE, pattern="S1") 

> S
 [1] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180412T171648_20180412T171715_021437_024E95_BDA1.zip"
 [2] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180424T171648_20180424T171715_021612_02540A_BB21.zip"
 [3] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180506T171649_20180506T171716_021787_025996_98AB.zip"
 [4] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180518T171649_20180518T171716_021962_025F27_A15C.zip"
 [5] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180530T171650_20180530T171717_022137_0264C8_5D94.zip"
 [6] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180611T171651_20180611T171718_022312_026A3D_BBFC.zip"
 [7] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180623T171652_20180623T171719_022487_026F7C_450E.zip"
 [8] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180705T171652_20180705T171719_022662_027499_1B8F.zip"
 [9] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180717T171653_20180717T171720_022837_0279EC_5E5E.zip"
[10] "/shared/Training/EARSEL0918_UrbanClassification_Germany/Original//S1A_IW_SLC__1SDV_20180729T171654_20180729T171721_023012_027F72_97F6.zip"

Using S as input, I want to create two new differnet lists. One containing the files in positions [1], [3],[5],[7],[9] and the other containing files in positions [2], [4],[6],[8],[10].

I am trying to adapt a previous code of mine. Here I create an empty list that I fill iterating over S but 1 by 1 and not in the way I want.

input<-list()
for (i in S){
  input[[i]]<-paste("-Pinput1=", i, sep="")
}

Do you have any suggestion. Something like i+2 ?

回答1:

Would this come close to what you need?

library(tidyverse)

list1 <- S[seq(1, 9, 2)] %>% 
  map(~paste0("-Pinput1=", .x))

The first line is extracting the odd positions from your list and the second one is pasting the string -Pinput1= in front of each

回答2:

Try this example:

S <- c("a", "b", "c", "d")

S_odd <- paste0("-Pinput1=", S[ c(TRUE, FALSE) ])
S_even <- paste0("-Pinput1=", S[ c(FALSE, TRUE) ])

S_odd
# [1] "-Pinput1=a" "-Pinput1=c"

S_even
# [1] "-Pinput1=b" "-Pinput1=d"

回答3:

Easiest way:

even_indexes<-seq(2,10,2) # List of even indexes
odd_indexes<-seq(1,10,2)  # List of odd indexes
paste0("-Pinput1=",df[odd_indexes,])  # Name with odd index
paste0("-Pinput1=",df[even_indexes,]) # Name with even index

回答4:

Adding all your ideas I managed to find a solution too:

input<-list()
for (i in S[seq(1, 10, 2)]){
  input[[i]]<-paste("-Pinput1=", i, sep="")
}

and

input<-list()
for (i in S[seq(2, 10, 2)]){
  input[[i]]<-paste("-Pinput1=", i, sep="")
}

来源：https://stackoverflow.com/questions/52218824/create-list-in-r-with-specific-iteration

标签

list

iteration