[R] Fetching a range of columns

[David Winsemius]

On Sep 14, 2008, at 7:20 PM, David Winsemius wrote:

>
> On Sep 14, 2008, at 5:39 PM, Adam D. I. Kramer wrote:
>
>>
>>
>> Not sure if the help you needed was using the comma, or the :  
>> syntax, or if
>> you're trying to read only certain columns during the read.csv  
>> process
>> (which I don't think that's possible).
>
> ? colClasses  # with the vector element of NULL for each unwanted  
> column.
>
> I am not the person to be advising how to do this properly, as all  
> of my efforts to use this facility to date have failed and I have  
> resorted to reading in lines  with as.is=TRUE and then post- 
> processing. But the facility does exist.
>
> Maybe someone could give me a clue how one might construct a vector  
> to send to colClasses inside read.table?
>
> > mt <- matrix(1:200,nrow=4)
> > write.table(file=file.choose(), as.data.frame(mt))
> > read.table(file.choose())
>  V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15 V16 V17 V18 V19  
> V20 V21 V22 V23 V24 V25 V26 V27 V28 V29
> 1  1  5  9 13 17 21 25 29 33  37  41  45  49  53  57  61  65  69   
> 73  77  81  85  89  93  97 101 105 109 113
> 2  2  6 10 14 18 22 26 30 34  38  42  46  50  54  58  62  66  70   
> 74  78  82  86  90  94  98 102 106 110 114
> 3  3  7 11 15 19 23 27 31 35  39  43  47  51  55  59  63  67  71   
> 75  79  83  87  91  95  99 103 107 111 115
> 4  4  8 12 16 20 24 28 32 36  40  44  48  52  56  60  64  68  72   
> 76  80  84  88  92  96 100 104 108 112 116
>  V30 V31 V32 V33 V34 V35 V36 V37 V38 V39 V40 V41 V42 V43 V44 V45 V46  
> V47 V48 V49 V50
> 1 117 121 125 129 133 137 141 145 149 153 157 161 165 169 173 177  
> 181 185 189 193 197
> 2 118 122 126 130 134 138 142 146 150 154 158 162 166 170 174 178  
> 182 186 190 194 198
> 3 119 123 127 131 135 139 143 147 151 155 159 163 167 171 175 179  
> 183 187 191 195 199
> 4 120 124 128 132 136 140 144 148 152 156 160 164 168 172 176 180  
> 184 188 192 196 200
>
> Not working efforts:
> tstdta <- read.table(file.choose(), colClasses =  
> c(c(paste(rep("NULL",49),sep=","),"numeric"),header=TRUE)
> tstdta <- read.table(file.choose(), colClasses = paste(rep("NULL", 
> 49),"numeric",sep=","),header=TRUE)


  Argument recycling. Paste returns 49 element vector, each with  
"NULL, numeric".

?append

 > tstdta <- read.table(file.choose(), colClasses = append( rep("NULL", 
48), c("numeric","numeric"), after=48), header=FALSE,  skip=1)

 > tstdta
   V49 V50
1 189 193
2 190 194
3 191 195
4 192 196

 > tstdta <- read.table(file.choose(), colClasses = append(rep("NULL", 
48),c("numeric","numeric"),after=45),header=FALSE, skip=1)
 > tstdta
   V46 V47
1 177 181
2 178 182
3 179 183
4 180 184

Setting header=TRUE created an error:
Error in read.table(file.choose(), colClasses = append(rep("NULL",  
49),  :
   invalid 'row.names' length

I am assuming that is because the number of columns in the data.frame  
did not match the vector of names extracted from the first row.

-- 
David Winsemius
Heritage Labs