It?s sometimes faster to ask from someone who has already learnt the syntax.
In this case one has to do e.g.
names(data$somecol)
To get the collection and then iteration through it is almost like in Python:
for(i in names(data$somecol)) {
# do something
}
> Bert Gunter <bgunter.4567 at gmail.com> kirjoitti 6.11.2017 kello
19.55:
>
> Time to go through a tutorial or two! -- This forum cannot replace such
self study.
>
> Your query evidences some basic confusion, but ?tapply or the equivalent
lapply(split(...)) construct are most likely relevant.
>
> 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 Mon, Nov 6, 2017 at 9:40 AM, mviljamaa <mviljamaa at kapsi.fi
<mailto:mviljamaa at kapsi.fi>> wrote:
> How can I do a for loop that does to a data.frame column what:
>
> for x in xs:
>
> does in Python?
>
> Obviously the data.frame column in question holds "levels". What
if the data.frame is in matrix form?
>
> BR, Matti
>
> ______________________________________________
> R-help at r-project.org <mailto:R-help at r-project.org> mailing list
-- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
<https://stat.ethz.ch/mailman/listinfo/r-help>
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>
[[alternative HTML version deleted]]
Except that syntax is wrong:> d <- data.frame (a = 1:3, b = letters[1:3]) > names(d$a)NULL -- Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Mon, Nov 6, 2017 at 11:26 AM, Matti Viljamaa <mviljamaa at kapsi.fi> wrote:> It?s sometimes faster to ask from someone who has already learnt the > syntax. > In this case one has to do e.g. > > names(data$somecol) > > To get the collection and then iteration through it is almost like in > Python: > > for(i in names(data$somecol)) { > # do something > } > > Bert Gunter <bgunter.4567 at gmail.com> kirjoitti 6.11.2017 kello 19.55: > > Time to go through a tutorial or two! -- This forum cannot replace such > self study. > > Your query evidences some basic confusion, but ?tapply or the equivalent > lapply(split(...)) construct are most likely relevant. > > Cheers, > Bert > > > > Bert Gunter > > "The trouble with having an open mind is that people keep coming along and > sticking things into it." > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) > > On Mon, Nov 6, 2017 at 9:40 AM, mviljamaa <mviljamaa at kapsi.fi> wrote: > >> How can I do a for loop that does to a data.frame column what: >> >> for x in xs: >> >> does in Python? >> >> Obviously the data.frame column in question holds "levels". What if the >> data.frame is in matrix form? >> >> BR, Matti >> >> ______________________________________________ >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide http://www.R-project.org/posti >> ng-guide.html <http://www.r-project.org/posting-guide.html> >> and provide commented, minimal, self-contained, reproducible code. >> > > >[[alternative HTML version deleted]]
Maybe you are thinking of the levels function rather than the names function? Which still presumes the column is a factor column, when it might actually be a character column (in which case you might use the unique function). Again, a reproducible example would stop the guessing. -- Sent from my phone. Please excuse my brevity. On November 6, 2017 11:26:24 AM PST, Matti Viljamaa <mviljamaa at kapsi.fi> wrote:>It?s sometimes faster to ask from someone who has already learnt the >syntax. >In this case one has to do e.g. > >names(data$somecol) > >To get the collection and then iteration through it is almost like in >Python: > >for(i in names(data$somecol)) { > # do something >} > >> Bert Gunter <bgunter.4567 at gmail.com> kirjoitti 6.11.2017 kello 19.55: >> >> Time to go through a tutorial or two! -- This forum cannot replace >such self study. >> >> Your query evidences some basic confusion, but ?tapply or the >equivalent lapply(split(...)) construct are most likely relevant. >> >> 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 Mon, Nov 6, 2017 at 9:40 AM, mviljamaa <mviljamaa at kapsi.fi ><mailto:mviljamaa at kapsi.fi>> wrote: >> How can I do a for loop that does to a data.frame column what: >> >> for x in xs: >> >> does in Python? >> >> Obviously the data.frame column in question holds "levels". What if >the data.frame is in matrix form? >> >> BR, Matti >> >> ______________________________________________ >> R-help at r-project.org <mailto:R-help at r-project.org> mailing list -- To >UNSUBSCRIBE and more, see >> https://stat.ethz.ch/mailman/listinfo/r-help ><https://stat.ethz.ch/mailman/listinfo/r-help> >> PLEASE do read the posting guide >http://www.R-project.org/posting-guide.html ><http://www.r-project.org/posting-guide.html> >> and provide commented, minimal, self-contained, reproducible code. >> > > > [[alternative HTML version deleted]] > >______________________________________________ >R-help at 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.
Hello,
If you want to loop through the columns of a data.frame you can do
for(i in names(df)){
[code]
}
Another way would be
lapply(names(df), function(somecol) class(df[[somecol]]))
where class(df[[somecol]]) is just an example, you would use whatever
fits your needs.
When you say that the column in question holds "levels" do you mean
it's
a factor? (factors are R's categorical variables.)
Hope this helps,
Rui Barradas
Em 06-11-2017 19:26, Matti Viljamaa escreveu:> It?s sometimes faster to ask from someone who has already learnt the
syntax.
> In this case one has to do e.g.
>
> names(data$somecol)
>
> To get the collection and then iteration through it is almost like in
Python:
>
> for(i in names(data$somecol)) {
> # do something
> }
>
>> Bert Gunter <bgunter.4567 at gmail.com> kirjoitti 6.11.2017 kello
19.55:
>>
>> Time to go through a tutorial or two! -- This forum cannot replace such
self study.
>>
>> Your query evidences some basic confusion, but ?tapply or the
equivalent lapply(split(...)) construct are most likely relevant.
>>
>> Cheers,
>> Bert
>>
>>
>>
>> Bert Gunter
>>
>> "The trouble with having an open mind is that people keep coming
along and sticking things into it."
>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic
strip )
>>
>> On Mon, Nov 6, 2017 at 9:40 AM, mviljamaa <mviljamaa at kapsi.fi
<mailto:mviljamaa at kapsi.fi>> wrote:
>> How can I do a for loop that does to a data.frame column what:
>>
>> for x in xs:
>>
>> does in Python?
>>
>> Obviously the data.frame column in question holds "levels".
What if the data.frame is in matrix form?
>>
>> BR, Matti
>>
>> ______________________________________________
>> R-help at r-project.org <mailto:R-help at r-project.org> mailing
list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
<https://stat.ethz.ch/mailman/listinfo/r-help>
>> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
<http://www.r-project.org/posting-guide.html>
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
Matti -
Since you are asking about looping through a column, not looping across columns,
it is simply the following:
# Note: data.frame() turns strings into factors by default.
myDF <- data.frame(type = c("a", "j", "a",
"a", "j"),
weight = c(12.3, 6.8, 10.5, NA, "5.5"))
myDF$type # ... is a vector of factors
for(type in myDF$type) {
print(type)
}
# or (less explicit in the code and will break if the order of columns
# ever changes):
for(type in myDF[ , 1]) {
print(type)
}
# In a matrix, all elemnts have to be of the same type. Let's make a
# matrix of characters:
myMat <- matrix(cbind(as.character(myDF$type),
c("red", "green", "red",
"red", "green")),
ncol = 2)
for(type in myMat[ , 1]) {
print(type)
}
As others have remarked, for added efficiency with large datasets we often use
functions from the apply() family, rather than for-loops.
I hope this helps,
Boris
PS: don't call your data frames "df" since df() is a function and
this may make your code hard to read.
> On Nov 6, 2017, at 2:49 PM, Rui Barradas <ruipbarradas at sapo.pt>
wrote:
>
> Hello,
>
> If you want to loop through the columns of a data.frame you can do
>
> for(i in names(df)){
> [code]
> }
>
> Another way would be
>
> lapply(names(df), function(somecol) class(df[[somecol]]))
>
> where class(df[[somecol]]) is just an example, you would use whatever fits
your needs.
>
> When you say that the column in question holds "levels" do you
mean it's a factor? (factors are R's categorical variables.)
>
> Hope this helps,
>
> Rui Barradas
>
>
> Em 06-11-2017 19:26, Matti Viljamaa escreveu:
>> It?s sometimes faster to ask from someone who has already learnt the
syntax.
>> In this case one has to do e.g.
>>
>> names(data$somecol)
>>
>> To get the collection and then iteration through it is almost like in
Python:
>>
>> for(i in names(data$somecol)) {
>> # do something
>> }
>>
>>> Bert Gunter <bgunter.4567 at gmail.com> kirjoitti 6.11.2017
kello 19.55:
>>>
>>> Time to go through a tutorial or two! -- This forum cannot replace
such self study.
>>>
>>> Your query evidences some basic confusion, but ?tapply or the
equivalent lapply(split(...)) construct are most likely relevant.
>>>
>>> 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 Mon, Nov 6, 2017 at 9:40 AM, mviljamaa <mviljamaa at kapsi.fi
<mailto:mviljamaa at kapsi.fi>> wrote:
>>> How can I do a for loop that does to a data.frame column what:
>>>
>>> for x in xs:
>>>
>>> does in Python?
>>>
>>> Obviously the data.frame column in question holds
"levels". What if the data.frame is in matrix form?
>>>
>>> BR, Matti
>>>
>>> ______________________________________________
>>> R-help at r-project.org <mailto:R-help at r-project.org>
mailing list -- To UNSUBSCRIBE and more, see
>>> https://stat.ethz.ch/mailman/listinfo/r-help
<https://stat.ethz.ch/mailman/listinfo/r-help>
>>> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
<http://www.r-project.org/posting-guide.html>
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at 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.
>>
>
> ______________________________________________
> R-help at 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.