[R] Question On Regex and DataFrame

[Jim Lemon]

Hi kalyan,
It is a bit difficult to work out what you want to do. However, there are
some things I can suggest. The gsub function is useful for changing strings
not assigning new values. If you want to delete a column of a data frame if
there are any NA values, you first want to check for NA values (let's call
your data frame x.df to avoid confusion):

x.df<-data.frame(a=sample(1:10,10),
 b=c(sample(1:10,9),NA),c=sample(1:10,10))
any(is.na(x.df[,1]))

will return TRUE if at least one element of the first column of x.df is NA.
Next you want to know how many columns there are in x.df:

ncols<-dim(x.df)[2]

Now you can step through the columns _backwards_ (so you don't change the
order of the columns you are testing) to delete any containing NA values:

for(column in ncols:1) if(any(is.na(x.df[,column]))) x.df[[column]]<-NULL

This leaves me with the first and third columns of x.df.

Jim

On Mon, Feb 22, 2016 at 4:43 AM, kalyan chakravarty <
kalyanchakravarty456 at gmail.com> wrote:

> Hi,
> I am new to R and learning the basics.so i came to know that data frame can
> store any data type as oppose to matrix which stores only numeric.My
> question is
> 1.)How to replace a particular pattern with new pattern in data frame.I
> tried something like
> x = as.data.frame(gsub(".*LINK.*","NA",file))........but the output is
> really weird it converts every thing in zeros and ones.
>
> what i actually want is DELETE ALL THE RANDOM COLUMS IN DF BASED ON ROW
> VALUE.
>
> file = read.csv("x.csv",header=T,sep=",")#read the file
> file[file == "LINK"] = NA #replaced row pattern with NA
> file[,colSums(is.na(file))==0] #deleting all colums which has na's
>
> This approach pretty much does the thing but i want to get familiar on how
> to use regular expressions over data frame.
> Any suggestions on which function/package/regex to use when dealing with
> DataFrame
>
> Sorry if this is a basic question.
> Thank you
>
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>
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