CODEWITHSUNDEEP
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Barnaby
Barnaby

Reputation: 1480

paste dataframe name with colnames

I have a dataframe called A. There are six columns in A. 

A
Dxa  Dxb  Dxc  Dxd  Dxe  Dxf

I am wondering how could I instruct to paste A$ prior to each column name. So A ends up being "A$Dxa A$Dxb A$Dxc A$Dxd A$Dxe A$Dxf"

This is to place in the expression below 

paste(colnames(A), collapse=" + ")

So it ends up as 

A$Dxa + A$Dxb  + A$Dxc + A$Dxd + A$Dxe + A$Dxf

Thank you

Upvotes: 0

Views: 3618

Answers (2)

josliber
josliber

Reputation: 44309

It looks like you're trying to add all the columns of a data frame. You can do this with the Reduce function or the rowSums function:

# Sample Data
A = data.frame(Dxa=1:3, Dxb=1:3, Dxc=2:4, Dxd=7:5, Dxe=c(0, 0, 100))
A
#   Dxa Dxb Dxc Dxd Dxe
# 1   1   1   2   7   0
# 2   2   2   3   6   0
# 3   3   3   4   5 100

# Add Columns
Reduce("+", A)
# [1]  11  13 115
rowSums(A)
# [1]  11  13 115
apply(A, 1, sum)
# [1]  11  13 115

Creating an expression with paste and then evaluating that expression is not a good way to sum the columns of a data frame.

Upvotes: 0

Rentrop
Rentrop

Reputation: 21497

A<-data.frame(Dxa=numeric(), Dxb=numeric(),  Dxc=numeric(),  
              Dxd=numeric(),  Dxe=numeric(),  Dxf=numeric() )
paste("A",colnames(A),sep="$", collapse=" + ")

result:

[1] "A$Dxa + A$Dxb + A$Dxc + A$Dxd + A$Dxe + A$Dxf"

EDIT: Alternatively you can use (as Tyler Rinker suggested)

paste0("A$",colnames(A), collapse=" + ")

Upvotes: 1

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