I have to work with a .csv file that comes like this:
"IDEA ID,""IDEA TITLE"",""VOTE VALUE"""
"56144,""Net Present Value PLUS (NPV+)"",1"
"56144,""Net Present Value PLUS (NPV+)"",1"
If I use read.csv, I obtain a data frame with one variable. What I need is a data frame with three columns, where columns are separated by commas. How can I handle the quotes at the beginning of the line and the end of the line?
I don't think there's going to be an easy way to do this without stripping the initial and terminal quotation marks first. If you have sed on your system (Unix [Linux/MacOS] or Windows+Cygwin?) then
read.csv(pipe("sed -e 's/^\"//' -e 's/\"$//' qtest.csv"))
should work. Otherwise
read.csv(text=gsub("(^\"|\"$)","",readLines("qtest.csv")))
is a little less efficient for big files (you have to read in the whole thing before processing it), but should work anywhere.
(There may be a way to do the regular expression for sed in the same, more-compact form using parentheses that the second example uses, but I got tired of trying to sort out where all the backslashes belonged.)
I suggest both removing the initial/terminal quotes and turning the back-to-back double quotes into single double quotes. The latter is crucial in case some of the strings contain commas themselves, as in
"1,""A mostly harmless string"",11"
"2,""Another mostly harmless string"",12"
"3,""These, commas, cause, trouble"",13"
Removing only the initial/terminal quotes while keeping the back-to-back quote leads the read.csv() function to produce 6 variables, as it interprets all commas in the last row as value separators. So the complete code might look like this:
data.text <- readLines("fullofquotes.csv") # Reads data from file into a character vector.
data.text <- gsub("^\"|\"$", "", data.text) # Removes initial/terminal quotes.
data.text <- gsub("\"\"", "\"", data.text) # Replaces "" by ".
data <- read.csv(text=data.text, header=FALSE)
Or, of course, all in a single line
data <- read.csv(text=gsub("\"\"", "\"", gsub("^\"|\"$", "", readLines("fullofquotes.csv", header=FALSE))))
Related
I have to read in a lot of CSV files automatically. Some have a comma as a delimiter, then I use the command read.csv().
Some have a semicolon as a delimiter, then I use read.csv2().
I want to write a piece of code that recognizes if the CSV file has a comma or a semicolon as a a delimiter (before I read it) so that I don´t have to change the code every time.
My approach would be something like this:
try to read.csv("xyz")
if error
read.csv2("xyz")
Is something like that possible? Has somebody done this before?
How can I check if there was an error without actually seeing it?
Here are a few approaches assuming that the only difference among the format of the files is whether the separator is semicolon and the decimal is a comma or the separator is a comma and the decimal is a point.
1) fread As mentioned in the comments fread in data.table package will automatically detect the separator for common separators and then read the file in using the separator it detected. This can also handle certain other changes in format such as automatically detecting whether the file has a header.
2) grepl Look at the first line and see if it has a comma or semicolon and then re-read the file:
L <- readLines("myfile", n = 1)
if (grepl(";", L)) read.csv2("myfile") else read.csv("myfile")
3) count.fields We can assume semicolon and then count the fields in the first line. If there is one field then it is comma separated and if not then it is semicolon separated.
L <- readLines("myfile", n = 1)
numfields <- count.fields(textConnection(L), sep = ";")
if (numfields == 1) read.csv("myfile") else read.csv2("myfile")
Update Added (3) and made improvements to all three.
A word of caution. read.csv2() is designed to handle commas as decimal point and semicolons as separators (default values). If by any chance, your csv files have semicolons as separators AND points as decimal point, you may get problems because of dec = "," setting. If this is the case and you indeed have separator as the ONLY difference between the files, it is better to change the "sep" option directly using read.table()
I am reading from an API into a CSV file.
I then use R to perform calculations on that data. I am using read.csv to read the data into R.
In a few cases, the last column of a row has a blank value so the row ends in a comma.
This causes read.csv to fail.
Short of writing a script to fix the file, is there any way to read the CSV with a row or rows ending with a trailing comma?
I see what I did wrong. Some of my CSV fields are enclosed in double quotes, however I failed to define a quote character in my read.csv statement.
Here is my corrected statement:
MyData <<- read.csv(file=“myfile.csv”, header=TRUE, stringsAsFactors=FALSE, sep=“,”, quote=“\””)
Note that the quote parameter is escaped with a backslash.
Thanks to all.
Take this CSV file:
ID,NAME,VALUE
1,Blah,100
2,"Has space",200
3,"Ends with quotes"",300
4,""Surrounded with quotes"",300
It loads just fine in most statistical programs (R, SAS, etc.) but in Excel the third row is misinterpreted because it has two quotation marks. Escaping the last quote as \" will also not work in Excel. The only way I have found so far is to replace the one double quote with two double quotes:
ID,NAME,VALUE
1,Blah,100
2,"Has space",200
3,"Ends with quotes""",300
4,"""Surrounded with quotes""",300
But that would render the file completely useless for all other programs (R, SAS, etc.)
Is there a way to format the CSV file where strings can begin or end with the same characters as that used to surround them, such that it would work in Excel as well as commonly used statistical software?
Your second representation is the normal way to generate a CSV file and so should be easy to work with in any software. See the RFC 4180 specifications. https://www.ietf.org/rfc/rfc4180.txt
So your second example represents this data:
Obs id name value
1 1 Blah 100
2 2 Has space 200
3 3 Ends with quotes" 300
4 4 "Surrounded with quotes" 300
If you want to represent it as a delimited file where none of the values are allowed to contain the delimiter (in other words NOT as a standard CSV file) than it would look like:
id,name,value
1,Blah,100
2,Has space,200
3,Ends with quotes",300
4,"Surrounded with quotes",300
But if you want to allow the values to contain the delimiter then you need some way to distinguish embedded delimiters from real delimiters. So the standard forces values that contain the delimiter to be quoted. But once you do that you also need to also add quotes around fields that contain the quote character itself (and double the embedded quotes) to avoid making an ambiguous file. For example the quotes in the 4th observation in your first file look like they are optional quotes around a value instead of part of the value.
Many programs try to handle ambiguous situations. For example SAS does not allow values to contain embedded line breaks so you will always get four observations with your first example file.
But EXCEL allows the embedding of the end of line character(s) inside of quoted values. So in your original file the value of the second field in the third observations looks like what you would start to get if you added quotes around this value:
Ends with quotes",300
4,"Surrounded with quotes",300
So instead of 4 complete observations of three fields values in each there are only three observations and the last observation has only two field values.
This is caused by the fact that escape character for " in Excel is "": Escaping quotes and delimiters in CSV files with Excel
A quick and simple workaround that comes to mind in R is to first read the content of the csv with readLines, then replace the double (escaped) double quotes with just one double quotes, and then read.table:
read.table(
text = gsub(pattern = "\"\"", "\"", readLines("data.csv")),
sep = ",",
header = TRUE
)
i have files with similar contents
!software version: $Revision$
!date: 07/06/2016 $
!
! from Mouse Genome Database (MGD) & Gene Expression Database (GXD)
!
MGI
I am using read.csv to read the files. But I need to skip the lines with "!" in the beginning. How can I do that?
The read.csv function and read.table that it is based on have an argument called comment.char which can be used to specify a character that if seen will ignore the rest of that line. Setting that to "!" may be enough to do what you want.
If you really need a regular expression, then the best approach is to read the file using readLines (or similar function), then apply the regular expression to the resulting vector of character strings to drop to unwanted elements (rows), then pass the result to the text argument to read.table (or use a text connection).
To calculate the first line that doesn't start with a !,
to_skip <- min(grep('^[^!]', trimws(readLines('file.csv'))))
df <- read.csv('file.csv', skip = to_skip)
I have a csv file with ~200 columns and ~170K rows. The data has been extensively groomed and I know that it is well-formed. When read.table completes, I see that approximately half of the rows have been imported. There are no warnings nor errors. I set options( warn = 2 ). I'm using 64-bit latest version and I increased the memory limit to 10gig. Scratching my head here...no idea how to proceed debugging this.
Edit
When I said half the file, I don't mean the first half. The last observation read is towards the end of the file....so its seemingly random.
You may have a comment character (#) in the file (try setting the option comment.char = "" in read.table). Also, check that the quote option is set correctly.
I've had this problem before how I approached it was to read in a set number of lines at a time and then combine after the fact.
df1 <- read.csv(..., nrows=85000)
df2 <- read.csv(..., skip=84999, nrows=85000)
colnames(df1) <- colnames(df2)
df <- rbind(df1,df2)
rm(df1,df2)
I had a similar problem when reading in a large txt file which had a "|" separator. Scattered about the txt file were some text blocks that contained a quote (") which caused the read.xxx function to stop at the prior record without throwing an error. Note that the text blocks mentioned were not encased in double quotes; rather, they just contained one double quote character here and there (") which tripped it up.
I did a global search and replace on the txt file, replacing the double quote (") with a single quote ('), solving the problem (all rows were then read in without aborting).