Find the next non blank value in SAS - sas

Question

I am trying to linearly interpolate values within a panel set data. So I am find the next non zero value within a variable if the current value of the variable is "."
For example if X = { 1, 2, . , . , . ,7), I want to store 7 as a variable "Y" and subject the lag value of X from it as the numerator of the slope. Can anyone help with this step?

Answer 1

If you cannot transpose your data, here is a way that will work for your given example:
data test;
input id $3. x best12.;
datalines;
AAA 1
BBB 2
CCC .
DDD .
EEE .
FFF 7
;
run;
data test2;
set test;
n = _n_;
if x ne .;
run;
data test3;
set test2;
lagx = lag(x);
lagn = lag(n);
if _n_ > 1 and n ne lagn + 1 then do;
postiondiff = n - lagn;
valuediff = x - lagx;
do i = (lagx + ((x-lagx)/(n-lagn))) to x by ((x-lagx)/(n-lagn));
x = i;
output;
end;
end;
else output;
keep x;
run;
data test4;
merge test test3 (rename = (x=newx));
run;
So we are basically rebuilding the variable with the interpolated values, then remerging it into the original dataset without a by variable which will line up all the new interpolated data with the missing points.

Answer 2

Is there a way you could transpose all your data? Interpolating like that is much easier when all the data you need is in a single observation. Like this:
data test;
input x best12.;
datalines;
1
2
.
.
.
7
;
run;
proc transpose data = test
out = test2;
run;
data test3;
set test2;
array xvalues {*} COL1-COL6;
array interpol {4,10} begin1-begin10 end1-end10 begposition1-begposition10 endposition1-endposition10;
rangenum = 1;
* Find the endpoints of the missing ranges;
do i = 1 to dim(xvalues);
if xvalues{i} ne . then lastknownx = xvalues{i};
else do;
interpol{1,rangenum} = lastknownx;
if interpol{3,rangenum} = . then interpol{3,rangenum} = i - 1;
end;
if i > 1 and xvalues{i} ne . then do;
if xvalues{i-1} = . then do;
interpol{2,rangenum} = xvalues{i};
interpol{4,rangenum} = i;
rangenum = rangenum + 1;
end;
end;
end;
* Interpolate;
rangenum = 1;
do j = 1 to dim(xvalues);
if xvalues{j} = . then do;
xvalues{j} = interpol{1,rangenum} + (j-interpol{3,rangenum})*((interpol{2,rangenum}-interpol{1,rangenum})/(interpol{4,rangenum}-interpol{3,rangenum}));
end;
else if j > 1 and xvalues{j} ne . then do;
if xvalues{j-1} = . then rangenum = rangenum + 1;
end;
end;
keep col1-col6;
run;
That can handle up to 10 different missing ranges per observation, though you could tweak the code to handle much more than that by creating bigger arrays.

Answer 3

The SAS data step reads a dataset one record at a time from top to bottom. So at record i, it can't access i+1 because it hasn't read it yet; it can only access i-1. Assume you have a dataset with a variable x.
data intrpl;
retain _x;
set yourdata;
by x notsorted;
if not missing(x) then do;
_x = x;
if last.x then do;
slope = _x - lag(_x);
output;
end;
end;
run;
Transposing can get kind of messy if x takes on a lot of values, so I recommend this method. I hope it helps!