[R] Fw: adding a column to data frame solving the replacement problem

[hoda rahmati]

     On Friday, February 26, 2016 2:17 PM, hoda rahmati <hodarahmati68 at yahoo.com> wrote:
 

 Hi,Thank you for your answer and sorry that I forgot to add the command I used, the command is:mydata$NewColumn <-- mydata$Sequence[mydata$Sequence=="%Seq%tse"and then the Error that I got.what I want to do after adding the new column is to plot the other two variables I have in my data frame(mydata) according to the color, and the color I want is just for "%Seq%tse" .do you have any idea?
Thanks Hoda 



       On Thursday, February 25, 2016 8:39 AM, PIKAL Petr <petr.pikal at precheza.cz> wrote:
 

 Hi

It seems to me that you misunderstand how objects (data.frames) in R work.

see in line

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of hoda
> rahmati via R-help
> Sent: Wednesday, February 24, 2016 3:39 PM
> To: r-help at r-project.org
> Subject: [R] adding a column to data frame solving the replacement
> problem
>
> Hi all,
>
> I have a data set (mydata) containing 471 variables. One of the columns
> looks as below
>
> $ Sequence : Factor w/ 3 levels "","%Seq%gre",..: 2 2 2 2 2 2 2 2 2 2

There is also missing value in this column. I am not sure if it is intended, it is your decision. To get missing values as really missing when importing data you shall explicitly use na identifier in read command, something like.

mydata <- read.*(something, na.string="")

from help page:
na.strings
a character vector of strings which are to be interpreted as NA values. Blank fields are also considered to be missing values in logical, integer, numeric and complex fields.

> ...
>
> sequence contains %Seq%gre and %Seq%tse and I extract only %Seq%tse and
> add it to my variables and plot a scatterplot of mydata. I use table
> and the result is: table(mydata$Sequence)
>  %Seq%gre %Seq%tse
>          1          25520          243744 in the next step I  want to
> add a column to my main data set (mydata) containing only %Seq%tse,
> however when I use the following command there's an error telling me:
> Error in `$<-.data.frame`(`*tmp*`, "NewColumn", value = c(3L, 3L, 3L,
>  :
>  replacement has 243744 rows, data has 269265 How can I add this
> column correctly to mydata? Thanks for any help

There is no command in your mail. However all columns in data frame has to have the same length, so when you add shorter vector it is recycled without error.

see
iris$aaa <- letters[1:5]
head(iris,10)

This simple command does not produce error.

I can get similar error

> iris[iris$aaa=="c", 1]<- iris[,2]

Error in `[<-.data.frame`(`*tmp*`, iris$aaa == "c", 1, value = c(3.5,  :
  replacement has 150 rows, data has 30

this results from operation in which I try add longer vector to shorter data frame.

To get more specific answer, you shall add exact command you used (maybe also a toy working example).


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And you shall post in plain text, not HTML.

Cheers
Petr

>
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