[R] How to parse a string into the symbol for a data frame object
I have several data frames, eg: df1 - data.frame(x=seq(0,10), y=seq(10,20)) df2 - data.frame(a=seq(0,10), b=seq(10,20)) It is common to create loops in R like this: for(df in list(df1, df2)){ #etc. } This works fine when you know the name of the objects to put into the list. I assume that the order of the objects in the list is respected through the loop. Inside the loop, the objects of the list are 'dereferenced' using 'df' but, to my knowledge, there is no way to tell whether 'df' is a current representation of 'df1' or 'df2' without some additional book keeping. In addition, I really want to use 'paste' within the loop to create a new string value that will have the symbol name of a data frame to be dereferenced, e.g.: for(n in c(1, 2)){ dfString - paste('df', n, sep=); print(eval(dfString)) } [1] df1 [1] df2 This is not what I want. I have read through the documentation on eval and similar commands like substitute and quote. I program regularly, but I do not understand these constructs in R. I do not understand the R framework for parsing and evaluation and I don't have a lot of time right now to get lost in this detail. I could really use some help to get the string values in my loop to be parsed into symbols that refer to the data frame objects df1 and df2. How is this done? Best, Darren __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] How to parse a string into the symbol for a data frame object
One way to do it is to pass in the character name of the dataframe you want to reference and then use 'get' to access the value: e.g., df1 - data.frame(x=seq(0,10), y=seq(10,20)) df2 - data.frame(a=seq(0,10), b=seq(10,20)) # use the character names for referencing for (df in c('df1', 'df2')){ # get the data to operate on (read-only) .val - get(df) # now you can reference the object print(names(.val)) # or construct new objects to store the value in # or you can use assign' to store back in the original object assign(paste('temp.', df, sep=''), .val) } On 8/19/07, Darren Weber [EMAIL PROTECTED] wrote: I have several data frames, eg: df1 - data.frame(x=seq(0,10), y=seq(10,20)) df2 - data.frame(a=seq(0,10), b=seq(10,20)) It is common to create loops in R like this: for(df in list(df1, df2)){ #etc. } This works fine when you know the name of the objects to put into the list. I assume that the order of the objects in the list is respected through the loop. Inside the loop, the objects of the list are 'dereferenced' using 'df' but, to my knowledge, there is no way to tell whether 'df' is a current representation of 'df1' or 'df2' without some additional book keeping. In addition, I really want to use 'paste' within the loop to create a new string value that will have the symbol name of a data frame to be dereferenced, e.g.: for(n in c(1, 2)){ dfString - paste('df', n, sep=); print(eval(dfString)) } [1] df1 [1] df2 This is not what I want. I have read through the documentation on eval and similar commands like substitute and quote. I program regularly, but I do not understand these constructs in R. I do not understand the R framework for parsing and evaluation and I don't have a lot of time right now to get lost in this detail. I could really use some help to get the string values in my loop to be parsed into symbols that refer to the data frame objects df1 and df2. How is this done? Best, Darren __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem you are trying to solve? __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] How to parse a string into the symbol for a data frame object
You might want to store the data frames in a list to eliminate this problem and make it more convenient to iterate over them: L - list(df1 = df1, df2 = df2) rm(df1, df2) # reduce each data frame to its first few rows for(nm in names(L)) L[[nm]] - head(L[[nm]) or if you don't need to modify them or know their names: # print first few lines of each for(df in L) print(head(df)) On 8/19/07, Darren Weber [EMAIL PROTECTED] wrote: I have several data frames, eg: df1 - data.frame(x=seq(0,10), y=seq(10,20)) df2 - data.frame(a=seq(0,10), b=seq(10,20)) It is common to create loops in R like this: for(df in list(df1, df2)){ #etc. } This works fine when you know the name of the objects to put into the list. I assume that the order of the objects in the list is respected through the loop. Inside the loop, the objects of the list are 'dereferenced' using 'df' but, to my knowledge, there is no way to tell whether 'df' is a current representation of 'df1' or 'df2' without some additional book keeping. In addition, I really want to use 'paste' within the loop to create a new string value that will have the symbol name of a data frame to be dereferenced, e.g.: for(n in c(1, 2)){ dfString - paste('df', n, sep=); print(eval(dfString)) } [1] df1 [1] df2 This is not what I want. I have read through the documentation on eval and similar commands like substitute and quote. I program regularly, but I do not understand these constructs in R. I do not understand the R framework for parsing and evaluation and I don't have a lot of time right now to get lost in this detail. I could really use some help to get the string values in my loop to be parsed into symbols that refer to the data frame objects df1 and df2. How is this done? Best, Darren __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.