CODEWITHSUNDEEP
r
Batool
Batool

Reputation: 1007

Extracting the value of an element from Dataframe in R

I am very new to R and trying to extract a specific element from a data frame and compare it with an integer.

I had a table saved in text file.

data-file image

I used the following to read the table.

mydata = read.table("file.txt");

In my case I want to compare an element say, say the first element of USERPOR (which is 1.0) with an integer 1.0 (so the comparison should return true).

The code I wrote was 

mydata[[2,7]]

[1] 1.000
Levels: 1.000 10.0000 2.000 3.000 4.00 5.00 6.000 7.000 8.000 9.000 USERPROR

However, when I compared them, I got 'FALSE'. Can anybody tell why is that so?

> mydata[[2,7]]==1.0

[1] FALSE

Upvotes: 0

Views: 309

Answers (1)

Russ Lenth
Russ Lenth

Reputation: 6760

Hmmmm. First, elements of a data.frame are ordinarily accessed using single brackets -- like mydata[2,7]. Double brackets will access a column, e.g. mydata[[2]] will return the second column. Thus, mydata[[7]][2] is the same as mydata[2,7].

Second, since your output includes a Levels: list, it appears that that variable is stored as a factor having levels of "1.000", "10.0000", ... "USERPROR" (odd enough that I'm guessing the data are entered incorrectly). Accordingly, I believe that in your example, mydata[2,7] == "1.000" would return TRUE.

In general, if you want to compare a numeric value with an integer, don't use a comparison value like 1.0, because thje .0 part forces it to be stored as floating-point, not integer. If the data are stored as floating-point, there may be enough roundoff that a number computed as 1.0 is not exactly equal to an integer 1. The reliable way to test it is to use round(mydata[2,7]) == 1.

Upvotes: 2

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