[R] Apply gsub to dataframe to modify row values

[Luigi Marongiu]

Thank you, it works!

On Mon, Aug 9, 2021 at 3:26 PM Andrew Simmons <akwsimmo using gmail.com> wrote:
>
> Hello,
>
>
> There are two convenient ways to access a column in a data.frame using `$` and `[[`. Using `df` from your first email, we would do something like
>
> df <- data.frame(VAR = 1:3, VAL = c("value is blue", "Value is red", "empty"))
> df$VAL
> df[["VAL"]]
>
> The two convenient ways to update / / replace a column with something new are also very similar, something like
>
> df$VAL <- ...
> df[["VAL"]] <- ...
>
> As for the regex part, I would suggest using `sub` instead of `gsub` since you're looking to remove only the first instance of "value is". Also, I would recommend using "^" to mark the beginning of your string, something like
>
> df$VAL <- sub("^Value is ", "", df$VAL, ignore.case = TRUE)
>
> I might be misunderstanding, but it sounds like you also want to remove all leading whitespace. If so, you could do something like
>
> df$VAL <- sub("^[[:blank:]]*Value is ", "", df$VAL, ignore.case = TRUE)
>
> where "*" signifies that there will be zero or more blank characters at the beginning of the string. You can try `?regex` to read more about this.
>
> I hope this helps!
>
> On Mon, Aug 9, 2021 at 6:50 AM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>>
>> Sorry, silly question, gsub works already with regex. But still, if I
>> add `[[:blank:]]` still I don't get rid of all instances. And I am
>> keeping obtaining extra columns
>> ```
>> > df[df$VAL] = gsub("[[:blank:]Value is]", "", df$VAL, ignore.case=TRUE)
>> > df[df$VAL] = gsub("[[:blank:]Value is]", "", df$VAL, ignore.case=TRUE);df
>>   VAR           VAL value is blue Value is red empty
>> 1   1 value is blue             b            b     b
>> 2   2  Value is red            rd           rd    rd
>> 3   3         empty          mpty         mpty  mpty
>> ```
>>
>> On Mon, Aug 9, 2021 at 12:40 PM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>> >
>> > Thank you, that is much appreciated. But on the real data, the
>> > substitution works only on few instances. Is there a way to introduce
>> > regex into this?
>> > Cheers
>> > Luigi
>> >
>> > On Mon, Aug 9, 2021 at 11:01 AM Jim Lemon <drjimlemon using gmail.com> wrote:
>> > >
>> > > Hi Luigi,
>> > > Ah, now I see:
>> > >
>> > >  df$VAL<-gsub("Value is","",df$VAL,ignore.case=TRUE)
>> > > df
>> > >  VAR   VAL
>> > > 1   1  blue
>> > > 2   2   red
>> > > 3   3 empty
>> > >
>> > > Jim
>> > >
>> > > On Mon, Aug 9, 2021 at 6:43 PM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>> > > >
>> > > > Hello,
>> > > > I have a dataframe where I would like to change the string of certain
>> > > > rows, essentially I am looking to remove some useless text from the
>> > > > variables.
>> > > > I tried with:
>> > > > ```
>> > > > > df = data.frame(VAR = 1:3, VAL = c("value is blue", "Value is red", "empty"))
>> > > > > df[df$VAL] = gsub("value is ", "", df$VAL, ignore.case = TRUE, perl = FALSE)
>> > > > > df
>> > > >   VAR           VAL value is blue Value is red empty
>> > > > 1   1 value is blue          blue         blue  blue
>> > > > 2   2  Value is red           red          red   red
>> > > > 3   3         empty         empty        empty empty
>> > > > ```
>> > > > which is of course wrong because I was expecting
>> > > > ```
>> > > >   VAR           VAL
>> > > > 1   1             blue
>> > > > 2   2             red
>> > > > 3   3            empty
>> > > > ```
>> > > > What is the correct syntax in these cases?
>> > > > Thank you
>> > > >
>> > > > ______________________________________________
>> > > > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> > > > 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.
>> >
>> >
>> >
>> > --
>> > Best regards,
>> > Luigi
>>
>>
>>
>> --
>> Best regards,
>> Luigi
>>
>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> 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.



-- 
Best regards,
Luigi