R help - May 2006 - How to choose columns in data.frame by parts of columns' names?

Dear all,

I have a data.frame which has names as following.
[1] "XG1"  "YG1"  "XEST"     "YEST"
[2] "XNOEMP1"  "XNOEMP2" "YNOEMP1" 
"YNOEMP2"
[3] "XBUS10"   "XBUS10A" "XBUS10B" 
"XBUS10C"
[4] "YBUS10"   "YBUS10A"  "YBUS10B" 
"YBUS10C"
[5] "XOWNBUS"  "XSELFEST"  "YOWNBUS" 
"YSELFEST"

Those columns have names beginning with "X" or "Y". Each
"X" is paired
by a "Y", e.g. "XG1" and "YG1", but they are not
in the order of "X Y
X Y ...". I want to combine "X*" and "Y*" like this:

data.new[,"G1"]  <- (data.old[,"XG1"] +
endata.use[,"YG1"])/2

How to choose columns by parts of names? For example, I can pick out
XG1 and YG1 because they have the common part "G1".

Thank you.

Wei-Wei

Wei-wei
> I have a data.frame which has names as following.
> [1] "XG1"  "YG1"  "XEST"     "YEST"
> [2] "XNOEMP1"  "XNOEMP2" "YNOEMP1" 
"YNOEMP2"
> [3] "XBUS10"   "XBUS10A" "XBUS10B" 
"XBUS10C"
> [4] "YBUS10"   "YBUS10A"  "YBUS10B" 
"YBUS10C"
> [5] "XOWNBUS"  "XSELFEST"  "YOWNBUS" 
"YSELFEST"
>
> Those columns have names beginning with "X" or "Y".
Each "X"
> is paired by a "Y", e.g. "XG1" and "YG1", but
they are not in
> the order of "X Y X Y ...". I want to combine "X*" and
"Y*" like this:
>
> data.new[,"G1"]  <- (data.old[,"XG1"] +
endata.use[,"YG1"])/2
>
> How to choose columns by parts of names? For example, I can pick out
> XG1 and YG1 because they have the common part "G1".
Not entirely sure what you mean but one approach might be to re-order
the columns so that they are in order.

yourNames
 [1] "XG1"      "YG1"      "XEST"    
"YEST"     "XNOEMP1"  "XNOEMP2"
 [7] "YNOEMP1"  "YNOEMP2"  "XBUS10"  
"XBUS10A"  "XBUS10B"  "XBUS10C"
[13] "YBUS10"   "YBUS10A"  "YBUS10B" 
"YBUS10C"  "XOWNBUS"  "XSELFEST"
[19] "YOWNBUS"  "YSELFEST"
yourNames[order(substring(yourNames,2), substring(yourNames, 1,1))]
 [1] "XBUS10"   "YBUS10"   "XBUS10A" 
"YBUS10A"  "XBUS10B"  "YBUS10B"
 [7] "XBUS10C"  "YBUS10C"  "XEST"    
"YEST"     "XG1"      "YG1"
[13] "XNOEMP1"  "YNOEMP1"  "XNOEMP2" 
"YNOEMP2"  "XOWNBUS"  "YOWNBUS"
[19] "XSELFEST" "YSELFEST"

gives an idea of what I mean .......

Peter Alspach



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On 5/30/06, Guo Wei-Wei <wwguocn at gmail.com>
wrote:
> Dear all,
>
> I have a data.frame which has names as following.
> [1] "XG1"  "YG1"  "XEST"     "YEST"
> [2] "XNOEMP1"  "XNOEMP2" "YNOEMP1" 
"YNOEMP2"
> [3] "XBUS10"   "XBUS10A" "XBUS10B" 
"XBUS10C"
> [4] "YBUS10"   "YBUS10A"  "YBUS10B" 
"YBUS10C"
> [5] "XOWNBUS"  "XSELFEST"  "YOWNBUS" 
"YSELFEST"
>
> Those columns have names beginning with "X" or "Y".
Each "X" is paired
> by a "Y", e.g. "XG1" and "YG1", but they are
not in the order of "X Y
> X Y ...". I want to combine "X*" and "Y*" like
this:
>
> data.new[,"G1"]  <- (data.old[,"XG1"] +
endata.use[,"YG1"])/2
>
> How to choose columns by parts of names? For example, I can pick out
> XG1 and YG1 because they have the common part "G1".
>

This gives all columns whose column name contains G1:

data.old[, regexpr("G1", colnames(data.old)) > 0]