CODEWITHSUNDEEP
rdataframe
Adam Erickson
Adam Erickson

Reputation: 6363

R: Converting a character list of object names that specify columns to a new data frame?

I've tried many things listed on this site, but nothing has yet answered this problem as far as I can tell.

I have a list of characters that specify object names within my workspace. Each of these objects represent separate columns that I would like to cbind into a new data frame.

I can do this manually very easily. However, I am having trouble getting the character list to convert into an object list bound together as columns in a new data frame. Here is the structure of the list:

list("ID", "ID1", "ID2", "ID3", "Year", "Month", "Element", "Value1", 
    "MFlag1", "QFlag1", "SFlag1", "Value2", "MFlag2", "QFlag2", 
    "SFlag2", "Value3", "MFlag3", "QFlag3", "SFlag3", "Value4", 
    "MFlag4", "QFlag4", "SFlag4", "Value5", "MFlag5", "QFlag5", 
    "SFlag5", "Value6", "MFlag6", "QFlag6", "SFlag6", "Value7", 
    "MFlag7", "QFlag7", "SFlag7", "Value8", "MFlag8", "QFlag8", 
    "SFlag8", "Value9", "MFlag9", "QFlag9", "SFlag9", "Value10", 
    "MFlag10", "QFlag10", "SFlag10", "Value11", "MFlag11", "QFlag11", 
    "SFlag11", "Value12", "MFlag12", "QFlag12", "SFlag12", "Value13", 
    "MFlag13", "QFlag13", "SFlag13", "Value14", "MFlag14", "QFlag14", 
    "SFlag14", "Value15", "MFlag15", "QFlag15", "SFlag15", "Value16", 
    "MFlag16", "QFlag16", "SFlag16", "Value17", "MFlag17", "QFlag17", 
    "SFlag17", "Value18", "MFlag18", "QFlag18", "SFlag18", "Value19", 
    "MFlag19", "QFlag19", "SFlag19", "Value20", "MFlag20", "QFlag20", 
    "SFlag20", "Value21", "MFlag21", "QFlag21", "SFlag21", "Value22", 
    "MFlag22", "QFlag22", "SFlag22", "Value23", "MFlag23", "QFlag23", 
    "SFlag23", "Value24", "MFlag24", "QFlag24", "SFlag24", "Value25", 
    "MFlag25", "QFlag25", "SFlag25", "Value26", "MFlag26", "QFlag26", 
    "SFlag26", "Value27", "MFlag27", "QFlag27", "SFlag27", "Value28", 
    "MFlag28", "QFlag28", "SFlag28", "Value29", "MFlag29", "QFlag29", 
    "SFlag29", "Value30", "MFlag30", "QFlag30", "SFlag30", "Value31", 
    "MFlag31", "QFlag31", "SFlag31")

Again, each of these are existing workspace objects I am trying to call as columns in a new data frame.

Edit:

Here is the code I used to create each of the vectors:

idCols  <- list("ID","ID1","ID2","ID3","Year","Month","Element")
varCols <- paste(rep(list("Value","MFlag","QFlag","SFlag"),31),rep(c(1:31),each=4),sep="")
allCols <- c(idCols,varCols)
allList <- as.list(paste(allCols))

These objects are only temporarily in the workspace, as they are nested within a custom function. However, I would love to hear more about creating lists of objects.

Upvotes: 1

Views: 2004

Answers (2)

Hong Ooi
Hong Ooi

Reputation: 57696

This avoids any coercion to/from a matrix:

data.frame(lapply(setNames(your_list, your_list), get))

Upvotes: 1

joran
joran

Reputation: 173677

This is sort of a shot in the dark:

x <- 1:5
y <- 1:5
> do.call(cbind,mget(c('x','y')))
     x y
[1,] 1 1
[2,] 2 2
[3,] 3 3
[4,] 4 4
[5,] 5 5

Note that you need the characters in a vector not a list, so use c() not list().

One weakness of this solution is that if each object is an atomic vector, the result will be a matrix. If all your data are numeric, this isn't a huge deal, you can simple coerce to a data frame using as.data.frame. But if you have some character vectors mixed in there, you will end up with a character matrix, with all the numeric vectors converted to character.

I believe this shortcoming can be fixed by using cbind.data.frame rather than just cbind.

But of course, the fact that you have that many objects floating around in your workspace is a very bad sign. Typically in R we try not to organize our objects that way. Much better have lists of related objects. Then you can operate on them quickly and compactly as a group using tools like lapply.

Upvotes: 3

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