recursive function on each pixel in google earth engine - google-earth-engine

Question

I want to filter time series in the google earth engine which requires two for loops over time-series of a single pixel. I searched around and not found any example related to this. I know about .map function and I am using it for the generation of RVI on the earth engine. I found about .toArray function but not found any example related to my problem.
I will appreciate any help in this regard. Also, I am new to the earth engine so this may be a trivial question for others.
This is the code that I have. I took it from a blog and modified it according to my need. I am stuck after this.
var sentinel1 = ee.ImageCollection('COPERNICUS/S1_GRD_FLOAT');
// Filter VH, IW
var vh = sentinel1
// Filter to get images with VV and VH dual polarization.
//.filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
// Filter to get images collected in interferometric wide swath mode.
.filter(ee.Filter.eq('instrumentMode', 'IW'))
// reduce to VH polarization
//.select('VH')
// filter 10m resolution
.filter(ee.Filter.eq('resolution_meters', 10));
// Filter to orbitdirection Descending
var vhDescending = vh.filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'));
// Filter time 2015
var vhDesc2015 = vhDescending.filterDate(ee.Date('2021-01-01'), ee.Date('2021-04-30'));
// Filter to MKD roi
var s1_mkd = vhDesc2015.filterBounds(roi);
print('All metadata:', s1_mkd);
var count = s1_mkd.size();
print('Count: ', count);
//var dates = s1_mkd.aggregate_array("system:time_start")
//print('dates: ', dates);
var dates = s1_mkd
.map(function(image) {
return ee.Feature(null, {'date': image.date().format('YYYY-MM-dd')})
})
.distinct('date')
.aggregate_array('date')
print('dates: ', dates);
var featureCollection = ee.FeatureCollection(dates
.map(function(element){
return ee.Feature(null,{prop:element})}))
//Export a .csv table of date, mean NDVI for watershed
Export.table.toDrive({
collection: featureCollection,
description: 'Timeseries',
folder: 'WC_raw',
fileFormat: 'CSV',
});
var rvi4s1 = function(img){
var vh = img.select('VH');
var vv = img.select('VV');
var col = vv.divide(vv.add(vh)).sqrt().rename('dop');
var dop = col.select('dop')
var value = dop.multiply(vh.multiply(4).divide(vv.add(vh))).rename('rvi4s1');
return value;
};
var rvi = s1_mkd.map(rvi4s1);
print(rvi);