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Fill in empty cell in data.frame from previous value

9 messages · Jim Lemon, Bert Gunter, Boris Steipe +3 more

#
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
#
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.

Jim

On Sun, Jun 25, 2017 at 3:49 AM, Christophe Elek
<christophe.elek at gmail.com> wrote:
#
You need to go through some tutorials, not expect us to tutor you
here. That is not the purpose of this list (although we do some of
this indirectly of course). There are many good online tutorials --
search or see here:  https://www.rstudio.com/online-learning/#R  . Or
start by going through the Intro to R tutorial that ships with R.

Cheers,
Bert
Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Sun, Jun 25, 2017 at 12:11 AM, Jim Lemon <drjimlemon at gmail.com> wrote:
#
Run it through a loop. I assume the cell contents is NA (Not Available). Test for it with is.na(). Whenever that returns TRUE, replace the NA value with the value from the previous row.

Cheers,
B.
#
Perfect Jim, that Is exactly what I needed ? let me check that ... 
Cheers

From: Jim Lemon
Sent: June 25, 2017 3:11 AM
To: Christophe Elek
Cc: r-help at r-project.org
Subject: Re: [R] Fill in empty cell in data.frame from previous value

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.

Jim

On Sun, Jun 25, 2017 at 3:49 AM, Christophe Elek
<christophe.elek at gmail.com> wrote:

  
  
#
Excellent Boris, thx ? this helps

From: Boris Steipe
Sent: June 25, 2017 11:23 AM
To: Christophe Elek
Cc: r-help at r-project.org
Subject: Re: [R] Fill in empty cell in data.frame from previous value

Run it through a loop. I assume the cell contents is NA (Not Available). Test for it with is.na(). Whenever that returns TRUE, replace the NA value with the value from the previous row.

Cheers,
B.

  
  
#
> ?fill

G?ran
On 2017-06-24 19:49, Christophe Elek wrote:
#
That's the kind of help that we like to provide. And for extra marks, you
can write a small function that will deal with consecutive NA values.

Jim

On Mon, Jun 26, 2017 at 1:25 AM, Christophe Elek <christophe.elek at gmail.com>
wrote:

  
  
#
Hi

Maybe I am missing something but in package "zoo" is function "na.locf", which fills empty cells with previous value.

So when you read your file

dat<-read.table("....", na="")

you can use

library(zoo)
sapply(dat, na.locf)

the only problem is that it changes factors to numeric representation. It is solved here

https://stackoverflow.com/questions/22771260/na-locf-converts-data-from-numeric-to-character

Cheers
Petr
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