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Gene Leynes

2009-Jul-22 00:39 UTC

[R] How to replace NAs in a vector of factors?

# Just when I thought I had the basic stuff mastered....
# This has been quite perplexing, thanks for any help


## Here's the example:

db1=data.frame(
    olditems=c('soup','','','','nuts'),
    prices=c(4.45, 3.25, 4.42, 2.25, 3.98))
db2=data.frame(
   
newitems=c('stew','crackers','tofu','goatsmilk','peanuts'))

str(db1)    #factors and prices
str(db2)    #new names, but I want *only* the updates

is.na(db1$olditems)  #a little surprising that '' is not equal to NA
db1$olditems==''     #oh good, at least I can get to the blanks this way
db1$olditems[db1$olditems=='']  #wait, only one item is returned?
db1[db1$olditems=='',]  #somehow this works!

#how would I get the new item names into the old items column of db1??
# I was expecting that this would work:
#    db1$olditems[db1$olditems=='']#       
db2$newitems[db1$olditems=='']

	[[alternative HTML version deleted]]

hadley wickham

2009-Jul-22 01:18 UTC

head link

[R] How to replace NAs in a vector of factors?

On Tue, Jul 21, 2009 at 7:39 PM, Gene Leynes<gleynes+r at gmail.com>
wrote:> # Just when I thought I had the basic stuff mastered....
> # This has been quite perplexing, thanks for any help
>
>
> ## Here's the example:
>
> db1=data.frame(
> ?
?olditems=c('soup','','','','nuts'),
> ? ?prices=c(4.45, 3.25, 4.42, 2.25, 3.98))
> db2=data.frame(
> ?
?newitems=c('stew','crackers','tofu','goatsmilk','peanuts'))
>
> str(db1) ? ?#factors and prices
> str(db2) ? ?#new names, but I want *only* the updates
>
> is.na(db1$olditems) ?#a little surprising that '' is not equal to
NA
Why?
> db1$olditems=='' ? ? #oh good, at least I can get to the blanks
this way
> db1$olditems[db1$olditems==''] ?#wait, only one item is returned?
length(db1$olditems[db1$olditems==''])
> db1[db1$olditems=='',] ?#somehow this works!
>
> #how would I get the new item names into the old items column of db1??
> # I was expecting that this would work:
> # ? ?db1$olditems[db1$olditems=='']> # ? ? ?
?db2$newitems[db1$olditems=='']
Try working with characters instead of factors.

db1$olditems <- as.character(db1$olditems)
db2$newitems <- as.character(db2$newitems)
db1$olditems[db1$olditems==''] <-
db2$newitems[db1$olditems=='']

Hadley

-- 
http://had.co.nz/

jim holtman

2009-Jul-22 01:21 UTC

head link

[R] How to replace NAs in a vector of factors?

Notice that three items are returned where you thought one was:

[1] FALSE  TRUE  TRUE  TRUE FALSE> db1$olditems[db1$olditems=='']  #wait, only one item is returned?[1]
Levels:  nuts soup> db1[db1$olditems=='',]  #somehow this works!  olditems prices
2            3.25
3            4.42
4            2.25> paste('[',db1$olditems[db1$olditems==''],']') # put
some characters around return values
[1] "[  ]" "[  ]" "[  ]">

The '[1]' was just an indication that this is the first value returned
and the other two were blanks so you did not see them.  Also "" is
just that; a blank and not NA.

On Tue, Jul 21, 2009 at 8:39 PM, Gene Leynes<gleynes+r at gmail.com>
wrote:> # Just when I thought I had the basic stuff mastered....
> # This has been quite perplexing, thanks for any help
>
>
> ## Here's the example:
>
> db1=data.frame(
> ?
?olditems=c('soup','','','','nuts'),
> ? ?prices=c(4.45, 3.25, 4.42, 2.25, 3.98))
> db2=data.frame(
> ?
?newitems=c('stew','crackers','tofu','goatsmilk','peanuts'))
>
> str(db1) ? ?#factors and prices
> str(db2) ? ?#new names, but I want *only* the updates
>
> is.na(db1$olditems) ?#a little surprising that '' is not equal to
NA
> db1$olditems=='' ? ? #oh good, at least I can get to the blanks
this way
> db1$olditems[db1$olditems==''] ?#wait, only one item is returned?
> db1[db1$olditems=='',] ?#somehow this works!
>
> #how would I get the new item names into the old items column of db1??
> # I was expecting that this would work:
> # ? ?db1$olditems[db1$olditems=='']> # ? ? ?
?db2$newitems[db1$olditems=='']
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

Bill.Venables at csiro.au

2009-Jul-22 01:22 UTC

head link

[R] How to replace NAs in a vector of factors?

Couple of points:

1. if you are going to be replacing entries in factors with updated levels,
it's probably easier if you start with your strings remaining as strings as
they go into the data frames.  So here is how I would start your example


db1 <- data.frame(
    olditems =
c('soup','','','','nuts'),
    prices = c(4.45, 3.25, 4.42, 2.25, 3.98), 
	stringsAsFactors = FALSE)
db2 <- data.frame(
    newitems =
c('stew','crackers','tofu','goatsmilk','peanuts'),
	stringsAsFactors = FALSE)


2. Strings with zero characters are still strings (like zero is still a number).
They are not missing.  If you want them to be made missing you can do so
afterwards with:


#### zero length strings become NA 
is.na(db1$olditems[db1$olditems == '']) <- TRUE


3. Now to replace the missing values with the corresponding ones from the second
data frame:


k <- is.na(db1$olditems)
db1[k, "olditems"] <- db2[k, "newitems"]


4. Check
> db1   olditems prices
1      soup   4.45
2  crackers   3.25
3      tofu   4.42
4 goatsmilk   2.25
5      nuts   3.98> 
5. If you really do want factors rather than character strings, you can now
change back:

db1 <- within(db1, olditems <- factor(olditems)) ## use <- here!

6. check the difference
> str(db1)'data.frame':   5 obs. of  2 variables:
 $ olditems: Factor w/ 5 levels "crackers","goatsmilk",..: 4
1 5 2 3
 $ prices  : num  4.45 3.25 4.42 2.25 3.98>  


Bill Venables
http://www.cmis.csiro.au/bill.venables/ 


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Gene Leynes
Sent: Wednesday, 22 July 2009 10:39 AM
To: r-help at r-project.org
Subject: [R] How to replace NAs in a vector of factors?

# Just when I thought I had the basic stuff mastered....
# This has been quite perplexing, thanks for any help


## Here's the example:

db1=data.frame(
    olditems=c('soup','','','','nuts'),
    prices=c(4.45, 3.25, 4.42, 2.25, 3.98))
db2=data.frame(
   
newitems=c('stew','crackers','tofu','goatsmilk','peanuts'))

str(db1)    #factors and prices
str(db2)    #new names, but I want *only* the updates

is.na(db1$olditems)  #a little surprising that '' is not equal to NA
db1$olditems==''     #oh good, at least I can get to the blanks this way
db1$olditems[db1$olditems=='']  #wait, only one item is returned?
db1[db1$olditems=='',]  #somehow this works!

#how would I get the new item names into the old items column of db1??
# I was expecting that this would work:
#    db1$olditems[db1$olditems=='']#       
db2$newitems[db1$olditems=='']

	[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
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.

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