How to find the measurements of same type in R

Question

I am new in R.I have one question regarding my data set.

 S.NO   Type Measurements
 1  1        2.1
 2  2        3.3
 3  2        3.1
 4  3        2.7
 5  3        2.6
 6  3        4.5
 7  2        1.1
 8  3        2.2

suppose we have measurements in column 3 but their types are given in column 2.Each measurement is either type 1,type 2 or type 3.Now if we are interested to find only measurements corressponding to type 2(suppose),how we can do it in R? I am looking forward to response.

Can you provide an example of your data.frame using the [dput function](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example)? — Robert Krzyzanowski, Nov 17 '14 at 15:37

score 2 · Answer 1 · answered Nov 17 '14 at 15:39

2

This is a basic subsetting question covered in most introductory R guides:

with(mydf, mydf[Type == 2, ])
#   S.NO Type Measurements
# 2    2    2          3.3
# 3    3    2          3.1
# 7    7    2          1.1
with(mydf, mydf[Type == 2, "Measurements"])
# [1] 3.3 3.1 1.1

You can also look at the subset function:

subset(mydf, subset = Type == 2, select = "Measurements")
#   Measurements
# 2          3.3
# 3          3.1
# 7          1.1

answered Nov 17 '14 at 15:39

A5C1D2H2I1M1N2O1R2T1

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I'm tempted to go find a duplicate. This is one of the most basic questions – Rich Scriven Nov 17 '14 at 15:47

score 1 · Answer 2 · answered Nov 17 '14 at 15:45

1

# make some data
testData$measurement=1:10
testData$Type=sample(1:3,10,replace=T)
testData=data.frame(testData)

# fetch only type 2
testData[testData$Type==2,]
# now only the measurements
testData[testData$Type==2,"measurement"]

answered Nov 17 '14 at 15:45

phonixor

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Other than the sample data, this doesn't seem to add anything I didn't cover -- Or am I missing something? – A5C1D2H2I1M1N2O1R2T1 Nov 17 '14 at 15:46
you are correct... expect that you used a `with` function that was not needed – phonixor Nov 17 '14 at 15:47
The `with` function actually makes the code much more readable, IMO – Rich Scriven Nov 17 '14 at 15:48
Saves me from typing a `$`, though the `nchar`s may not be significantly different. – A5C1D2H2I1M1N2O1R2T1 Nov 17 '14 at 15:48
@phonixor, it's pretty easy to benchmark. Check out the `microbenchmark` package if the microseconds really matter to you (because it's not going to add up to more than that, in either approach's favor). – A5C1D2H2I1M1N2O1R2T1 Nov 17 '14 at 16:05
@AnandaMahto for the record your method is slightly faster...`system.time(replicate(10000,with(testData, testData[Type == 2, "measurement"]))) system.time(replicate(10000,testData[testData$Type==2,"measurement"])) ` – phonixor Nov 17 '14 at 16:14

How to find the measurements of same type in R

2 Answers2