Как вернуть одно поле из всех функций?

Question

Мне нужно вернуть все функции для одного поля и только это одно поле, а не весь набор данных.

Мой файл JSON имеет следующий формат:

{"type":"FeatureCollection","crs":{"type":"name","properties":{"name":"urn:ogc:def:crs:OGC:1.3:CRS84"}},"features":[{"type":"Feature","properties":{"NAME":"Kingston upon Thames","GSS_CODE":"E09000021","HECTARES":3726.117,"NONLD_AREA":0,"ONS_INNER":"F","SUB_2009":null,"SUB_2006":null,"Area_name":"Kingston upon Thames","Inner_Outer_London":"Outer London","GLA_Population_Estimate_2015":170900,"GLA_Household_Estimate_2015":66870.... , 

{"type":"Feature","properties":{"NAME":"Croydon","GSS_CODE":"E09000008","HECTARES":8649.441,"NONLD_AREA":0,"ONS_INNER":"F","SUB_2009":null,"SUB_2006":null,"Area_name":"Croydon","Inner_Outer_London":"Outer London","GLA_Population_Estimate_2015":380700,"GLA_Household_Estimate_2015":152750,"Inland_Area_Hectares":8650.4,"Population_density_per_hectare_2015":44,"Average_Age_2015":36.8,"Proportion_of_population_aged_0-15_2015":22.1... 

EDIT: JSON через JSon пуха (слишком большой, чтобы даже копировать вставить 5% из них)

{ 
"type": "FeatureCollection", 
"crs": { 
    "type": "name", 
    "properties": { 
     "name": "urn:ogc:def:crs:OGC:1.3:CRS84" 
    } 
}, 
"features": [{ 
    "type": "Feature", 
    "properties": { 
     "NAME": "Kingston upon Thames", 
     "GSS_CODE": "E09000021", 
     "HECTARES": 3726.117, 
     "NONLD_AREA": 0, 
     "ONS_INNER": "F", 
     "SUB_2009": null, 
     "SUB_2006": null, 
     "Area_name": "Kingston upon Thames", 
     "Inner_Outer_London": "Outer London", 
     "GLA_Population_Estimate_2015": 170900, 
     "GLA_Household_Estimate_2015": 66870, 
     "Inland_Area_Hectares": 3726.1, 
     "Population_density_per_hectare_2015": 45.9, 
     "Average_Age_2015": 36.9, 
     "Proportion_of_population_aged_0-15_2015": 19, 
     "Proportion_of_population_of_working-age_2015": 68.1, 
     "Proportion_of_population_aged_65_and_over_2015": 12.9, 
     "Net_internal_migration_2014": -188, 
     "Net_international_migration_2014": 2136, 
     "Net_natural_change_2014": 1178, 
     "PC_of_resident_population_born_abroad_2014": 29.2, 
     "Largest_migrant_population_by_country_of_birth_2011": "Sri Lanka", 
     "PC_of_largest_migrant_population_2011": 2.2, 
     "Second_largest_migrant_population_by_country_of_birth_2011": "India", 
     "PC_of_second_largest_migrant_population_2011": 1.8, 
     "Third_largest_migrant_population_by_country_of_birth_2011": "Korea (South)", 
     "PC_of_third_largest_migrant_population_2011": 1, 
     "PC_of_population_from_BAME_groups_2013": 27, 
     "PC_people_aged_3_whose_main_language_is_not_English_2011_Census": 16.4, 
     "Overseas_nationals_entering_the_UK_NINo_2014_15": 3157, 
     "New_migrant_NINo_rates_2014_15": 27.6, 
     "Largest_migrant_population_arrived_during_2014_15": "Bulgaria", 
     "Second_largest_migrant_population_arrived_during_2014_15": "Poland", 
     "Third_largest_migrant_population_arrived_during_2014_15": "Romania", 
     "Employment_rate_PC_2014": 75, 
     "Male_employment_rate_2014": 81.6, 
     "Female_employment_rate_2014": 68.5, 
     "Unemployment_rate_2014": 5.3, 
     "Youth_Unemployment_claimant_rate_18-24_Dec-14": 3, 
     "Proportion_of_16-18_year_olds_who_are_NEET_PC_2014": 3.9, 
     "Proportion_of_the_working-age_population_who_claim_out-of-work_benefits_PC_May-2014": 7, 
     "PC_working-age_with_a_disability_2014": 13.8, 
     "Proportion_of_working_age_people_with_no_qualifications_PC_2014": 3, 
     "Proportion_of_working_age_with_degree_or_equivalent_and_above_PC_2014": 57.8, 
     "Gross_Annual_Pay_2014": 36700, 
     "Gross_Annual_Pay_-_Male_2014": 39359, 
     "Gross_Annual_Pay_-_Female_2014": 30144, 
     "Modelled_Household_median_income_estimates_2012_13": 56920, 
     "PC_adults_that_volunteered_in_past_12_months_2010_11_to_2012_13": 42.7, 
     "Number_of_jobs_by_workplace_2013": 82300, 
     "PC_of_employment_that_is_in_public_sector_2013": 17.8, 
     "Jobs_Density_2013": 1, 
     "Number_of_active_businesses_2013": 8130, 
     "Two-year_business_survival_rates_started_in_2011": 79, 
     "Crime_rates_per_thousand_population_2014_15": 58.5, 
     "Fires_per_thousand_population_2014": 1.8, 
     "Ambulance_incidents_per_hundred_population_2014": 11.1, 
     "Median_House_Price_2014": 385000, 
     "Average_Band_D_Council_Tax_charge_2015_16": 1674.7, 
     "New_Homes_net_2013_14": 260, 
     "Homes_Owned_outright_2014_PC": 27.7, 
     "Being_bought_with_mortgage_or_loan_2014_PC": 39, 
     "Rented_from_Local_Authority_or_Housing_Association_2014_PC": 10.7, 
     "Rented_from_Private_landlord_2014_PC": 22.4, 
     "PC_of_area_that_is_Greenspace_2005": 36.4, 
     "Total_carbon_emissions_2013": 752.4, 
     "Household_Waste_Recycling_Rate_2013_14": 46.3, 
     "Number_of_cars_2011_Census": 70421, 
     "Number_of_cars_per_household_2011_Census": 1.1, 
     "PC_of_adults_who_cycle_at_least_once_per_month_2013_14": 21.1, 
     "Average_Public_Transport_Accessibility_score_2014": 2.9, 
     "Achievement_of_5_or_more_A*-_C_grades_at_GCSE_or_equivalent_including_English_and_Maths_2013_14": 68.6, 
     "Rates_of_Children_Looked_After_2014": 33, 
     "PC_of_pupils_whose_first_language_is_not_English_2014": 31.2, 
     "PC_children_living_in_out-of-work_households_2014": 8.9, 
     "Male_life_expectancy_2011-13": 81.3, 
     "Female_life_expectancy_2011-13": 84.5, 
     "Teenage_conception_rate_2013": 15.8, 
     "Life_satisfaction_score_2011-14_out_of_10": 7.3, 
     "Worthwhileness_score_2011-14_out_of_10": 7.7, 
     "Happiness_score_2011-14_out_of_10": 7.4, 
     "Anxiety_score_2011-14_out_of_10": 3.3, 
     "Childhood_Obesity_Prevalance_PC_2013_14": 15.4, 
     "People_aged_17_with_diabetes_PC": 4.9, 
     "Mortality_rate_from_causes_considered_preventable": 147.8, 
     "Political_control_in_council": "Cons", 
     "Proportion_of_seats_won_by_Conservatives_in_2014_election": 58.3, 
     "Proportion_of_seats_won_by_Labour_in_2014_election": 4.2, 
     "Proportion_of_seats_won_by_Lib_Dems_in_2014_election": 37.5, 
     "Turnout_at_2014_local_elections": 43.1 
    }, 
    "geometry": { 
     "type": "MultiPolygon", 
     "coordinates": [ 
      [ 
       [ 
        [-0.330679021773025, 51.32901101084708], 
        [-0.330594407566612, 51.329088040122315], 
        [-0.330506076681679, 51.329148829750466], 
        [-0.33040917032063, 51.32920859781458], 
        [-0.330292080679783, 51.329270775839156], 
        [-0.329913420803488, 51.32946051567418], 
        [-0.329633553448498, 51.3296570587963], 
        [-0.329428743663152, 51.32984208225338], 
        [-0.329320874515433, 51.32996643949609], 
        [-0.329214439452638, 51.330090817097144], 
        [-0.329116282383711, 51.330263872520085], 
        [-0.329112914578128, 51.330396015110445], 
        [-0.329171126538274, 51.33072957024903], 
        [-0.329191261142089, 51.330965462528575], 
        [-0.329302869370564, 51.33152819023752], 
        [-0.329362730358861, 51.33161896966427], 
        [-0.329554511157394, 51.33187169808366], 
        [-0.32957894743785, 51.332186786094184], 
        [-0.329594169463172, 51.33228142503257], 
        [-0.329689958909293, 51.33248961989663], 
        [-0.329719262840317, 51.332670788169274], 
        [-0.329718670292571, 51.3327661008151], 
        [-0.329713610148521, 51.33286584602793], 
        [-0.329643333783058, 51.33349612124335], 
        [-0.329628931512944, 51.33385292028404], 
        [-0.32955045530859, 51.33415574945231], 
        [-0.329484343656736, 51.334355340533264], 
        [-0.329546392185782, 51.33446503536734], 
        [-0.32943190788577, 51.334850082388876], 
        [-0.329410693783327, 51.33511775790784], 
        [-0.329359189787204, 51.33531036319948], 
        [-0.329208182584011, 51.33563373967703], 
        [-0.329197301934782, 51.335933036465214], 
        [-0.3292123737182, 51.33630824086913], 
        [-0.329192093632385, 51.33670812012244], 
        [-0.329041495932886, 51.33757285371855], 
        [-0.328900403109473, 51.33817603945666], 
        [-0.328869185702877, 51.33867917682473], 
        [-0.328882267763104, 51.33903007285105], 
        [-0.328865474006543, 51.33941291579552], 
        [-0.328870743501784, 51.339583849376474], 
        [-0.328876209135269, 51.33974939022238], 
        [-0.328959278855396, 51.34011027719941], 
        [-0.32897922859697, 51.34023286043202], 
        [-0.328909131031345, 51.34077860720778], 
        [-0.32878050967231, 51.34107802245298], 
        [-0.328542139079097, 51.34174996140999], 
        [-0.328525372819542, 51.34177669979828], 
        [-0.328346097965183, 51.34204751484793], 
        [-0.328201229588486, 51.34231971993927], 
        [-0.328010139783513, 51.3429545638654], 
        [-0.327944151115631, 51.343347495330974], 
        [-0.327906765100805, 51.34374353279829], 
        [-0.327796114780899, 51.34390381902136], 
        [-0.327480771031571, 51.34400722741141], 
        [-0.328177350406429, 51.34404145110161], 
        [-0.328483504737766, 51.344545805494214], 
        [-0.328666777138526, 51.344915316212365], 
        [-0.32889842247652, 51.34529720700365], 
        [-0.329205727742453, 51.345888803363664], 
        [-0.329345801048439, 51.34614349149164], 
        [-0.329970752009771, 51.34728006692206], 
        [-0.330327238877941, 51.34790203652441], 
        [-0.330533821707245, 51.3484211522831], 
        [-0.330367226671742, 51.348579744260604], 
        [-0.330215568888878, 51.34876192950989], 
        [-0.33010259433868, 51.34898603165988], 
        [-0.329936935927235, 51.349237259467515], 
        [-0.329751960800545, 51.34954576382794], 
        [-0.329563227290772, 51.34991806127805], 
        [-0.329472923004122, 51.350071445078235], 
        [-0.329311170759688, 51.35033351873695], 
        [-0.329035951591489, 51.350714473637105], 
        [-0.328765226477058, 51.351129663623325], 
        [-0.328353064876424, 51.351721786146854], 
        [-0.328046476146282, 51.35213556344137], 
        [-0.327946973892058, 51.352186299935575], 
        [-0.327759713433126, 51.35228074629348], 
        [-0.327275573431615, 51.352522028103955], 
        [-0.326841759688993, 51.352800896109116], 
        [-0.326479944940916, 51.353034929194735], 
        [-0.32576608192508, 51.35335295635771], 
        [-0.324837670800118, 51.353725463631605], 
        [-0.324453895670668, 51.35389173249815], 
        [-0.324158745463219, 51.35410872689187], 
        [-0.323752687942134, 51.354413159704905], 
        [-0.323535036520884, 51.35467082857294], 
        [-0.323184811812359, 51.355176591871896], 
        [-0.32286192079005, 51.35552357765017], 
        [-0.322576060678597, 51.355839618929], 
        [-0.322259713883874, 51.35620378257071], 
        [-0.321952974065641, 51.35661934039564], 
        [-0.321529222971824, 51.35721037383058], 
        [-0.321217561495061, 51.35768161289952], 
        [-0.320948159097397, 51.358096803885], 
        [-0.32074485191113, 51.35839334104852], 
        [-0.320259404554301, 51.35909948913235], 
        [-0.320079309555563, 51.3594287310578], 
        [-0.320178298703104, 51.35954975110903], 
        [-0.320165137159728, 51.35959542427937], 
        [-0.319956965481558, 51.359632006261116], 
        [-0.319792373194367, 51.35992999621074], 
        [-0.319546591138533, 51.360484007640004], 
        [-0.319408576659198, 51.360919064677674], 
        [-0.319187471491333, 51.36162270524168], 
        [-0.319060204553952, 51.362313303737686], 
        [-0.318285367823378, 51.36350628288284], 
        [-0.318304692373129, 51.36368461225171], 
        [-0.318410288479828, 51.364684298029104], 
        [-0.318436574395861, 51.36533933091015], 
        [-0.318446928565835, 51.36540962119001], 
        [-0.318522194031934, 51.365864823752055], 
        [-0.318523331127983, 51.366186772301226], 
        [-0.318419501486083, 51.366982019317454], 
        [-0.318293959925026, 51.36789925275619], 
        [-0.318118776705997, 51.36891648952965], 
        [-0.318016869219867, 51.36958047277866], 
        [-0.31792307432635, 51.3697877525771], 
        [-0.317915189904803, 51.369846090732615], 
        [-0.317905671937818, 51.36990980094361], 
        [-0.318029423835983, 51.370296457234964], 
        [-0.317949485943705, 51.37063522667972], 
        [-0.317747858873623, 51.371236628787635], 
        [-0.317505451116108, 51.371970534099816], 
        [-0.317485004351317, 51.37201880004826], 
        [-0.317397736511194, 51.37220459108471], 
        [-0.317284276827518, 51.37243856545665], 
        [-0.31710915300419, 51.37270852331906], 
        [-0.316949159320968, 51.37291844843032], 
        [-0.31669434018152, 51.37316747730857], 
        [-0.316426180103382, 51.373388437150716], 
        [-0.31622441906802, 51.37356179105688], 
        [-0.315991741423486, 51.373755383037754], 
        [-0.31566786597181, 51.37396744709197], 
        [-0.315222750497486, 51.374233520531305], 
        [-0.31478304313528, 51.37443042773603], 
        [-0.314341466820288, 51.374638996680865], 
        [-0.313886319633562, 51.374669316927424], 
        [-0.313377130221505, 51.374684469452525], 
        [-0.31296052429465, 51.374721635667065], 
        [-0.312674896375059, 51.37475259344767], 
        [-0.312510458790253, 51.374770008772465], 
        [-0.312155172284965, 51.37481974553786], 
        [-0.311542017783552, 51.37492691452625], 
        [-0.31108965287778, 51.374998629591076], 
        [-0.310483753449209, 51.375142766954085], 
        [-0.309642711208725, 51.375312285083936], 
        [-0.309096994839523, 51.3753826456651], 
        [-0.308695083240137, 51.37544968412024], 
        [-0.308457219737233, 51.37586080533736], 
        [-0.308342125073947, 51.376059676775654], 
        [-0.307993631387426, 51.376665236570894], 
        [-0.307964589950761, 51.37706318563219], 
        [-0.307842121582618, 51.37753981880234], 
        [-0.307892155265686, 51.378365154948014], 
        [-0.307388502353935, 51.3783848578608], 
        [-0.307520636068388, 51.379009947771415], 
        [-0.308301986382553, 51.38003288908768], 
        [-0.308325982763562, 51.38008359360354], 
        [-0.308517491830129, 51.38050181237386], 
        [-0.309276738904714, 51.3804489235838], 
        [-0.309318630671963, 51.38110598120351], 
        [-0.309245493241462, 51.3811408959084], 
        [-0.309282222270164, 51.38131408205096], 
        [-0.309293558960914, 51.38135740967078], 
        [-0.309317283472768, 51.38149353886625], 
        [-0.309300461368501, 51.381638075513614], 
        [-0.309302186977275, 51.38170824197235], 
        [-0.309330928191318, 51.38186422705928], 
        [-0.309498364267572, 51.38184416158862], 
        [-0.309558079241459, 51.38244662180848], 
        [-0.309654600932123, 51.382518155823895], 
        [-0.309751942685852, 51.38264545512327], 
        [-0.309842559115887, 51.38283830261783], 
        [-0.309886786708619, 51.38284703382125], 
        [-0.309911349075752, 51.382882458877866], 
        [-0.310347176087456, 51.38365220797289], 
        [-0.310288338333552, 51.38380603058168], 
        [-0.310307294453304, 51.38395468024451], 
        [-0.31041283493994, 51.38421068996167], 
        [-0.310442912142391, 51.38425248916564], 
        [-0.310540822314576, 51.38436450868583], 
        [-0.310654513111652, 51.38451632264458], 
        [-0.310566458115827, 51.38460497812067], 
        [-0.310580338529139, 51.38465733476053], 
        [-0.31063098206852, 51.3847650756968], 
        [-0.310665004889603, 51.38481682347486], 
        [-0.310729833733766, 51.38489059736828], 
        [-0.310950016955934, 51.38503855072464], 
        [-0.311127228786578, 51.38514361955623], 
        [-0.311787662820079, 51.385786208624666], 
        [-0.310868910629078, 51.38618752238585], 
        [-0.311409329096351, 51.386733062833684], 
        [-0.311458857237744, 51.38679312704089], 
        [-0.311499998462655, 51.386846775623816], 
        [-0.311363961797792, 51.386911359771595], 
        [-0.311693817532641, 51.38712563803517], 
        [-0.311822993635975, 51.38720843162237], 
        [-0.3117687866668, 51.3872364266419], 
        [-0.311735086833573, 51.387253926103], 
        [-0.31184550451329, 51.38737781488004], 
        [-0.31174002919236, 51.387432048754796], 
        [-0.312872428617744, 51.388490588702766], 
        [-0.313158544399437, 51.38880045260526], 
        [-0.313188957535943, 51.38883326338753], 
        [-0.313348146628585, 51.3887645141297], 
        [-0.315981046740714, 51.38763335801295], 
        [-0.316518343718128, 51.388266056660285], 
        [-0.316599042794471, 51.38845605832363], 
        [-0.316617277106647, 51.388585812140974], 
        [-0.316816040880735, 51.388574279405724], 
        [-0.316811782773372, 51.38861198670033], 
        [-0.316809818612619, 51.38862634647098], 
        [-0.316805824328563, 51.38865686356263], 
        [-0.316800426521383, 51.38868646124439], 
        [-0.316792155711511, 51.38871601765691], 
        [-0.31677817187624, 51.38874459275521], 
        [-0.316759878524943, 51.38877310594719], 
        [-0.316716538003206, 51.388818345067065], 
        [-0.316663273809364, 51.3888598446173], 
        [-0.316605798959337, 51.38889858590655], 
        [-0.31654548398803, 51.38893638711643], 
        [-0.316489643363005, 51.38896975633323], 
        [-0.316425150631468, 51.389003900464004], 
        [-0.31635785076633, 51.38903620572856], 
        [-0.315848095181505, 51.38925818893088], 
        [-0.315457631909052, 51.38948008640397], 
        [-0.314980758945598, 51.38974570252308], 
        [-0.314134077472051, 51.39021821967621], 
        [-0.314273949435976, 51.39036231326585], 
        [-0.314682226633619, 51.3907512659625], 
        [-0.314819872857466, 51.39091690883333], 
        [-0.314926939104345, 51.39105423508098], 

Скажем, если пользователь хочет вернуть HECTARES для всех функций вместе с сопроводительным именем, какой код мне нужно использовать?

Пример: пользователь вводит га и выход возвращается что-то вроде: Kingston Upon Thames: 3726.117, Кройдон: 8649.441 и т.д.

Пример2: пользователь вводит GSS_CODE и выходные возвращает что-то вроде: Kingston Upon Thames: "E09000021", Кройдон: «E09000008» и т.д.

Мой код до сих пор выглядит следующим образом:

app.get("/api/boroughs_field", function(req, res){ 

    // read input parameter from request 
    var field = req.query['field']; 

    // validate input, check if the parameter is valid or not 
    if (field === undefined) 
    { 
     // return error as a JSON string 
     var str = JSON.stringify({"error":"Parameter 'field' is not defined."}); 
     res.end(str); 
    } 

    var fldObj = null; 

    // make a loop for fields??? 

    if (fldObj == null) 
    { 
     // field not found, return an error as a JSON string 
     var str = JSON.stringify({"error":"field '"+name+"' doesn't exist. Please check the spelling."}); 
     res.end(str); 
    } 

    // If the program gets here, the borough has been found. 
    var respJson = {}; 
    respJson["results"] = [ fldObj ]; 
    res.end(JSON.stringify(respJson)); 
    }); 
} 

так что да, я действительно не знаю, как закодировать петлю, чтобы получить нужный результат

Answer 1

Вы можете перебрать список возможностей и поиск имущества объектов с .hasOwnProperty('propName'):

var feature; 
var features = []; 

for(var i = 0, total = jsonObj.features.length; i < total; i++) { 
    feature = jsonObj.features[i]; 
    if (feature.hasOwnProperty(field)) { 
     features.push({ name: feature.name, value: feature[field] }); 
    } 
} 

Я рекомендую вам взглянуть на lodash для больше возможностей и производительности.

Answer 2

Итак, я думаю, вы хотите что-то вроде ниже. Я оставил много окружающих деталей, и их несколько нюансов, но это общий ответ на ваш вопрос.

var i, fLength, fieldValue, nameValue; 
// HECTARES, GSS_CODE, etc 
var requestedFieldName = ???; 
// Not quite understanding your return object so you'll have to figure this out 
var features = something.features; 
// an array of what you were looking for 
var res = []; 

// Standard loop, instead of checking the length every loop though 
// we set it as a constant to start with and check that constant. 
for (i=0, fLength = features.length; i<fLength; i++) { 
    // Javascript objects are a hashmap by their nature, 
    // normally you can use dot notation myVar.myVal, 
    // but that only works when myVal is a constant string. 
    // If it is a variable, as in this case you can use [] instead. 
    fieldValue = features[i][requestedFieldName]; 
    nameValue = features[i]["NAME"]; 
    res.push({"field":fieldValue", "name":nameValue}); 
}