[R] Working with < and > is data sets

[David L Carlson]

Here is one way to fix the data:

# First note that "value" is a factor so we need to convert it to character
> str(zp)
'data.frame':   20 obs. of  2 variables:
 $ variable: Factor w/ 5 levels "ZP.1","ZP.3",..: 1 1 1 1 2 2 2 2 3 3 ...
 $ value   : Factor w/ 19 levels "<0.030","<1.2",..: 3 4 2 1 7 8 6 5 12 11 ...
> zp$value <- as.character(zp$value)
> str(zp)
'data.frame':   20 obs. of  2 variables:
 $ variable: Factor w/ 5 levels "ZP.1","ZP.3",..: 1 1 1 1 2 2 2 2 3 3 ...
 $ value   : chr  "1160" "27.3" "<1.2" "<0.030" ...

# Next we need to see which values are preceded by "<", and record that in 
# a new variable, "note"
> zp$note <- ifelse(grepl("<", zp$value), "Limit", "Measured")

# Finally we strip the "<" off and convert "value" to numeric
> zp$value <- as.numeric(gsub("<", "", zp$value))
> str(zp)
'data.frame':   20 obs. of  3 variables:
 $ variable: Factor w/ 5 levels "ZP.1","ZP.3",..: 1 1 1 1 2 2 2 2 3 3 ...
 $ value   : num  1160 27.3 1.2 0.03 1870 45.7 0.85 0.025 695 31.9 ...
 $ note    : chr  "Measured" "Measured" "Limit" "Limit" ...
> head(zp)
  variable   value     note
1     ZP.1 1160.00 Measured
2     ZP.1   27.30 Measured
3     ZP.1    1.20    Limit
4     ZP.1    0.03    Limit
5     ZP.3 1870.00 Measured
6     ZP.3   45.70 Measured

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Sam Albers
Sent: Monday, January 26, 2015 12:41 PM
To: r-help at r-project.org
Subject: [R] Working with < and > is data sets

Hello,

I am having some trouble figuring out how to deal with data that has some
observations that are detection limits and others that are integers denoted
by greater and less than symbols. Ideally I would like a column that has
the data as numbers then another column with values "Measured" or "Limit"
or something like that. Data and further clarification below.

##Data
zp<-structure(list(variable = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L,
3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L),
                                        .Label = c("ZP.1", "ZP.3", "ZP.5",
"ZP.7", "ZP.9"), class = "factor"),
                   value = structure(c(3L, 4L, 2L, 1L, 7L, 8L, 6L, 5L, 12L,
11L, 10L, 9L, 15L, 16L, 14L, 13L, 19L, 18L, 17L, 9L),
                                     .Label = c("<0.030", "<1.2", "1160",
"27.3", "<0.025", "<0.85", "1870", "45.7", "<0.0020",
                                                "<0.050", "31.9", "695",
"<0.0060", "<0.20", "311", "8.84", "<0.090", "12", "646"), class =
"factor")),
              .Names = c("variable", "value"), row.names = c(NA, -20L),
class = "data.frame")

## As expected converting everything to numeric results is a slew of NA
values
zp$valuefactor<-as.numeric(as.character(zp$value))

## At this point I am unsure how to proceed.

zp

###

So I am just wondering how folks deal with this type of data. Any advice
would be much appreciated as I am looking for something that will reliably
works on a large data set.

Thanks in advance!

Sam

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