[ncl-talk] CSV file script

[Kevin Hallock]

Hi Grace,

It looks like you’re trying to run the example script csv_2.ncl <http://www.ncl.ucar.edu/Applications/Scripts/csv_2.ncl> from the NCL website. Here’s a link <http://ncl.ucar.edu/Applications/Data/> to all of the sample data files we host; specifically, you may want to download example2.csv <http://ncl.ucar.edu/Applications/Data/asc/example2.csv> if you don’t already have it.

A quick issue I’d like to mention: this example seems to be using “group” as a variable name, but recent versions of NCL treat “group” as a keyword (meaning it cannot be used as a variable). I will try to update this example on our website in the near future. For now, please use “grp” instead of “group” as needed.

In this example, a CSV file “example2.csv” is read into NCL using asciiread(). Then, the function str_get_field() is used repeatedly to store the 1st, 5th, and 9th values of each row into the variables “name”, “grp”, and “size”, respectively. If you were to add a “print(name)” line after “name = str_get_field(lines,1,delim)”, you should see output like this:
> print(name)

Variable: name
Type: string
Total Size: 56 bytes
            7 values
Number of Dimensions: 1
Dimensions and sizes:   [7]
Coordinates: 
(0)     psmith01
(1)     smehta
(2)     mrsjohns
(3)     psmith02
(4)     scohen
(5)     swright
(6)     amarkov

Similarly, printing the other variables, you would see:
> print(grp) 

Variable: grp
Type: integer
Total Size: 28 bytes
            7 values
Number of Dimensions: 1
Dimensions and sizes:   [7]
Coordinates: 
(0)     1
(1)     1
(2)     -1
(3)     0
(4)     2
(5)     1
(6)     3

and
> print(size)

Variable: size
Type: float
Total Size: 28 bytes
            7 values
Number of Dimensions: 1
Dimensions and sizes:   [7]
Coordinates: 
(0)      1
(1)     2.1
(2)      2
(3)     10
(4)      1
(5)      1
(6)      1

NCL is able to concatenate strings with other data types, which is what we see in the "print("Name is'" + name + "', group is " + grp + ", size is " + size)” statement. What is actually happening under the hood is something like this:
           / psmith01 \               / 1 \              /  1  \
          // smehta   \\             // 1 \\            // 2.1 \\
         /// mrsjohns \\\           ///-1 \\\          ///  2  \\\
"Name is -   psmith02  - , group is     0    , size is     10     "
         \\\ scohen   ///           \\\ 2 ///          \\\  1  ///
          \\ swright  //             \\ 1 //            \\  1  //
           \ amarkov  /               \ 3 /              \  1  /

or in NCL:
print("Name is'" + name + "', group is " + grp + ", size is " + size) 
(0)     Name is'psmith01', group is 1, size is 1
(1)     Name is'smehta', group is 1, size is 2.1
(2)     Name is'mrsjohns', group is -1, size is 2
(3)     Name is'psmith02', group is 0, size is 10
(4)     Name is'scohen', group is 2, size is 1
(5)     Name is'swright', group is 1, size is 1
(6)     Name is'amarkov', group is 3, size is 1


I hope this helps,
Kevin

> On Oct 23, 2017, at 4:14 PM, Grace Choi <gracesh27 at gmail.com> wrote:
> 
> Hi everyone,
> 
> So I am having a trouble understanding a part of a script for reading CSV file. 
> 
> I have been having a hard time getting this script to work, because I am not sure how to correctly write the highlighted part of the script. 
> 
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
> 
> begin
> filename = "example2.csv"
> 
> lines = asciiread(filename,-1,"string")
> 
> delim = ","
> 
> name = str_get_field(lines,1,delim)
> group = tointeger(str_get_field(lines,5,delim)
> size = tofloat(str_get_field(lines,9,delim)
> 
> print("Name is'" + name + "', group is " + group + ", size is " + size)
> end
> 
> I am not sure what print("Name is'" + name + "', group is " + group + ", size is " + size) indicates... What is the difference between "Name is"' + name. With an actual value put in, what should this script actually look like? 
> 
> Thanks so much for your help.
> 
> Sincerely,
> Grace
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