[R] Fill in empty cell in data.frame from previous value

Jim Lemon drjimlemon at gmail.com
Sun Jun 25 09:11:28 CEST 2017

Hi Chris,
You may know about the *apply family of functions. These slice various
data structures and "apply" a specified function to each slice,
usually returning a list of return values. As far as I am aware, you
can't access adjacent rows unless you reformat the data structure.

There is a way to do this particular job. It requires the sequence
operator (:), the ifelse function and indexing. What you do is to
create a sequence of all the values in the element "names", then
subtract 1 for all the NA (or any other specified value) values and
use the resulting vector to index the original element "names". It
won't work if the first value is NA, nor will it work for more than
one NA in a row. I realize that this is pretty obscure, but you said
that you didn't just want the solution. It's a one-liner.


On Sun, Jun 25, 2017 at 3:49 AM, Christophe Elek
<christophe.elek at gmail.com> wrote:
> Hello Total newbie here... I hope I read the guide properly
> I have the following data.frame (I read it from a CSV file I cannot change)
>   names val
> 1 Mandy   1
> 2         2
> 3 John    2
> 4         2
> I want to read the row number 2, but I want the first column to be “Mandy” and not null
> print (frame[2,])
> 2 Mandy   2
> I can manipulate the data.frame once loaded
> How can I fill all cell in column “names” with the previous value ?
> Or is there a function that will get me the row and fill the “names” column ?
> NOTA BENE: I do not want the answer, I want to find it myself but I need guidance
> If there is a function, tell me the library and I will search
> If this is an algorithm, tell me generally how you would do and let me scratch my head first 😊
> Thanks Chris
>         [[alternative HTML version deleted]]
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