Create and process several columns with loop in R

Question

I'm quite new to R and I would like to learn how to write a Loop to create and process several columns.

I imported a table into R that cointains data with 23 variables. For all of these variables I want to calculate the per capita valuem multiply this with 1000 and either write the data into a new table or in the same table as the old data.

So to this for only one column my operation looked like this:

<i>agriculture<-cbind(agriculture,"Total_value_per_capita"=agriculture$Total/agriculture$Total.Population*1000)</i>

Now I'm asking how to do this in a Loop for the 23 variables so that I won't have to write 23 similar lines of code.

I think the solution might look quite similar to the code pasted in this thread:

loop to create several matrix in R (maybe using paste)

but I dind't got it working on my code.

So any suggestion would be very helpful.

You can put cbind inside a loop. If your table's 23 variables are in 23 columns, just loop over the column number rather than label. E.g., cbind(agriculture, agriculture$Total/agriculture[,j]*1000) where j is the loop index. — Carl Witthoft
– Carl Witthoft, Commented Oct 30, 2012 at 13:17
Thanks for your reply. I tried to do it like this: agriculture<-cbind(agriculture, "Total_value_per_capita"=agriculture[,24]/agriculture$Total.Population*100 but it dindt work out. There was only one new column build with some strange numbers (I think maybe the product of all values over the prevoius columns...) — Joschi
– Joschi, Commented Oct 30, 2012 at 14:11

Beasterfield · Accepted Answer · 2012-10-30 13:22:22Z

1

I would always favor an appropriate *ply function over loops in R. In this case sapply could be your friend:

df <- data.frame( a=sample(10), b=sample(10), c=sample(10) )
df.per.capita <– as.data.frame(
  sapply(
    df[ colnames(df) != "c" ], function(x){ x/df$c *1000 }
  )
)

For more complicated cases, you should definitely have a look at the plyr package.

answered Oct 30, 2012 at 13:22

Beasterfield

7,1332 gold badges43 silver badges49 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Joschi Over a year ago

all right. this one worked out for me. Thanks a LOT!!! The only thing i maybe would like to improve is to automaticly get the columns since with this method here I still had to put all the paths in code i.e. data.frame(a=...,b=...c=...d=...). So the code still got a little bit crowded since i have 23 columns...

Beasterfield Over a year ago

I'm sorry but I am not sure if I got your question right. Which column names do you mean? The names of the input data.frame (df) or the resulting data.frame (df.per.capita)? Would something like names(df.per.capita) <- paste(names(df.per.capita), "_per_capita", sep="") help you?

Joschi Over a year ago

I ment the header of the columns to be calculated. But I just figured it out today by simply defining the whole table at once as the dataframe df<-data.frame(agriculture) Thank you for your help!!

Jilber Urbina · Accepted Answer · 2012-10-30 13:33:31Z

1

This can be done using sweep function. Using Beasterfield's data generation but setting the seed you can obtain the same results

set.seed(001)
df <- data.frame( a=sample(10), b=sample(10), c=sample(10) )
per.capita <- sweep(df[,colnames(df) != "c"], 1, STATS=df$c, FUN='/')*1000
per.capita
           a          b
1   300.0000   300.0000
2  2000.0000  1000.0000
3   833.3333  1000.0000
4  7000.0000 10000.0000
5   222.2222   555.5556
6  1000.0000   875.0000
7  1285.7143  1142.8571
8  1200.0000   800.0000
9  3333.3333   333.3333
10  250.0000  2250.0000

Comparing with Beasterfield's results:

all.equal(df.per.capita, per.capita)
[1] TRUE

answered Oct 30, 2012 at 13:33

Jilber Urbina

61.4k10 gold badges116 silver badges141 bronze badges

Collectives™ on Stack Overflow

Create and process several columns with loop in R

2 Answers 2

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related