Reading numbers as strings

Question

I am new at R programming and I want to read a text file in R.

One of the columns, lets say column 7 is numeric and each number represent an ID I want R to read the numbers as if they were strings. And count the number of times each ID appear in the file (such that later I can assign the frequency of each ID to the given ID for latter use) I have tried

mydata<-(read.table(filename.txt))
ID=mydata[7]
freq=table(ID)

This works but it takes the IDs as numbers. Now I have tried

freq=table(as.character(ID))

But then it takes the whole column ID as only one string and from

summary(freq)

I get

Number of cases in table: 1 
Number of factors: 1 

Answer 1

At the time of reading the data into your data frame from the text file you can specify the type of each column using the colClasses argument. See below a file have in my computer:

> head(read.csv("R/Data/ZipcodeCount.csv"))
    X zipcode stateabb countyno  countyname
1   1     401       NY      119 WESTCHESTER
2 391     501       NY      103     SUFFOLK
3 392     544       NY      103     SUFFOLK
4 393     601       PR        1    ADJUNTAS
5 630     602       PR        3      AGUADA
6 957     603       PR        5   AGUADILLA
> head(read.csv("R/Data/ZipcodeCount.csv",colClasses=c(rep("factor",5))))
    X zipcode stateabb countyno  countyname
1   1   00401       NY      119 WESTCHESTER
2 391   00501       NY      103     SUFFOLK
3 392   00544       NY      103     SUFFOLK
4 393   00601       PR      001    ADJUNTAS
5 630   00602       PR      003      AGUADA
6 957   00603       PR      005   AGUADILLA

> zip<-read.csv("R/Data/ZipcodeCount.csv",colClasses=c(rep("factor",5)))
> str(zip)
'data.frame':   53424 obs. of  5 variables:
 $ X         : Factor w/ 53424 levels "1","10000081",..: 1 36316 36333 36346 43638 52311 19581 23775 26481 26858 ...
 $ zipcode   : Factor w/ 41174 levels "00401","00501",..: 1 2 3 4 5 6 6 7 8 9 ...
 $ stateabb  : Factor w/ 60 levels "","  ","AK","AL",..: 41 41 41 46 46 46 46 46 46 46 ...
 $ countyno  : Factor w/ 380 levels "","000","001",..: 106 95 95 3 5 7 5 7 7 9 ...
 $ countyname: Factor w/ 1925 levels "","ABBEVILLE",..: 1844 1662 1662 9 10 11 10 11 11 12 ...
> head(table(zip[,"zipcode"]))

00401 00501 00544 00601 00602 00603 
    1     1     1     1     1     2 

as you can see R is no longer treating zipcodes as numbers but as factors. In your case you need to specify the class of the first 6 columns and then choose factor as your seventh. So if the first 6 columns are numeric it should be something like this colClasses = c(rep("numeric",6),"factor").

Answer 2

without the as.character your table should work correctly(i.e. freq <- table(ID)) , Quoting from ?table, your input can be:

one or more objects which can be interpreted as factors (including character strings), or a list (or data frame) whose components can be so interpreted. (For as.table and as.data.frame, arguments passed to specific methods.)

Answer 3

I think you missed the comma in your dataframe.

mydata<-(read.table(filename.txt))
ID=mydata[,7]  #added comma
freq=table(as.character(ID))